Despite the overall solid and stable market of classic cars, there are some cars that have actually lost value. Especially over the last decade, lots of people have invested in classic cars, but some media outlets are reporting an average drop of 10% when it comes to classic car prices. For example, Coutts Passion Index, an organization that records market trends of expensive collectibles, reports a decline in the classic car sector.

How is it possible to monitor the market trends of our favorite classics? Well, classic car insurance company Hagerty offers a valuation tool that gives a clear outline of how those trends fluctuate. Let's take a closer look at some cars that have seen their values drop significantly over the last 3 years.

Related: These 10 Italian Sports Cars Are Actually Cheap... For A Reason

8 1970 Buick Riviera GS - 2018: $20,000 - Today: $14,400

1970 Buick Riviera GS
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The Buick Riviera has a special role in the golden-era muscle cars fleet. Due to the high-end nature of this car, it received a warm welcome since its very first release. It wasn't a muscle car like the others: its luxury interior, completed by wooden details and fine leather seats, made the Riviera stand out.

1970 Buick Riviera GS side
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Also in 1970, the Gran Sport package was available: Strato bucket front seats and console automatic shifter were included. The Riviera wasn't only about details, but it was a car of substance: its bulky 455 cu in engine developed 370 hp and this GS model could do 0-60 mph in 7.9 seconds. Over the last 3 years though, its average price dropped significantly.

7 1957 Ford Thunderbird - 2018: $40,000 - Today: $29,400

1957 Ford Thunderbird, red with whitewall tyres
Mecum Auctions

The 1957 Ford Thunderbird was a fresh drop everybody fell in love with. The car wasn't excessively oversized, rather, the two-seater came in a well-proportioned design. The removable top, as well as the panoramic windshield, were highly appreciated among the young drivers.

1957 Ford Thunderbird, side
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In the 1957 model, the 292 cu in V8 engine was improved by mating it to twin McColloch superchargers. This stock modification aimed to increase the power outlet to 300 hp and 340 lb-ft of torque. Transmission options were a 3-speed manual, an overdrive version, and a Ford-O-Matic automatic transmission. Although the average price for a perfectly mint condition Thunderbird is about $63,500, according to Hagerty.com, the average price for a "Good condition" is about $29,400.

Related: These Are The Best Race Cars From The ’50s

6 1957 Pontiac Bonneville - 2018: $112,500 - Today: $73,200

1957 Pontiac Bonneville, fron
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The Pontiac Bonneville was only produced in 1956 and 1957. First of all, it's a very expensive car. The reason why its price has always been higher than its competitors was the limited production, which gave birth to 630 units only. Each of the 630 was destined to each domestic Pontiac dealership.

1957 Pontiac Bonneville, extra wheel on the back
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The Bonneville presented some outstanding features that were pretty uncommon on most of the mid-fifties' cars. Everything was electrically powered: steering, brakes, windows, antenna, and seats. The Rochester fuel-injected 347 cu in V8 could deliver some 315 hp. In September 2018 you could find a Bonneville in good condition for roughly $112,500. Today, it's rated at about $73,200.

Related: These Restored Classics Are Surprisingly Cheap

5 Porsche 911 Carrera (Turbo 930) - 2018: $115,500 - Today: $81,500

Porsche 911 Carrera turbo (930)
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The Porsche 911 Carrera Turbo was a real game-changer. Also called the 930, the most important aspect of this car was — of course — the turbocharged engine. Naturally-aspired air-cooled Porsche engines were already great examples of mechanic art, and the turbocharger contributed to making this car a one-of-a-kind sports car, for both good and bad.

Porsche 911 Carrera turbo (930) red, rear
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It wasn't an easy car to drive, the accentuated turbo-lag was unpredictable, especially for inexperienced drivers, as the extra power provided by the turbo was brutally insane. The 3.3-liter version of the 930 could do 0-60 in just 4.9 seconds, embarrassing most of the Ferraris or Corvettes available at the time. Although it's still an expensive car, its valuation has undergone a significant drop.

4 1965 Jaguar E-Type SI 4.2 - 2018: $120,000 - Today: $102,000

1967Jaguar E-Type SI 4.2 Roadster, grey, front
Mecum Auctions

In response to the American Corvettes and the German Porsches, Jaguar released the stunningly beautiful E-Type, which was also called "the most beautiful car ever made" by Enzo Ferrari himself. Presented at the 1961 Geneva Motor Show, the speechless audience was amazed by its aircraft-inspired lines and some innovative technical solutions.

1967Jaguar E-Type SI 4.2 Roadster, grey, rear
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The Jaguar E-Type was bought by people like Steve McQueen, Brigitte Bardot, and George Best, becoming a true icon of the Sixties. In September 2019, a Jaguar E-Type in good condition reached its best valuation ever of over $130,000. Now, the same dream car is rated at about $102,000.

3 1953-1954 Cadillac Eldorado - 2018: $162,500 - Today: $121,000

1954 Cadillac Eldorado, light blue
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The Cadillac Eldorado was the most luxurious model produced by the car manufacturer up to that time. Every single detail of the car bears a sense of fanciness, starting from the car's name. Some say the "Eldorado" was suggested in reference to the mythical city of gold. Some others reported that the name was chosen after the "Eldorado Country Club" located in the Coachella Valley, California, the favorite holiday location of the GM's top management.

1954 Cadillac Eldorado, light blue, rear
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Apart from the divergent ideas about its name's origin, it was a matter of fact that the Eldorado was one of the highest-end cars available in the USA at that time. Some features of this car were the frameless windows and the peculiar chrome profile along the sides, style choices from which car manufacturers would take inspiration for future models.

2 1969 Ford Mustang Boss 429 - 2018: $225,000 - Today: $162,000

1969 dark olive Ford Mustang Boss 429
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Among the greatest muscle cars introduced in 1969, the Boss version presented some features that made it stand out from the entry-level muscle or pony cars. The Ford Mustang Boss is packing a bulky 429 cu in V8 engine. Fitting the huge big block into a Mustang required some technical modification, such as significant changes to steering and suspension systems.

1969 Ford Mustang Boss 429 dark olive, rear
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This high-performance Mustang, which was originally intended for NASCAR races, could make up to 375 hp. The heavily modified motor, in fact, was one of the best offerings from Ford in the sports car market before the strict regulations on homologation arrived later in the '70s.

1 1958 Ferrari 250 California LWB - 2018: $12,500,000 - Today: $9,300,000

Ferrari 250 California LWB greay with decals
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One of the most desirable Ferrari of all time is the 250 California. The 2-seater came in two different wheelbase versions: a short wheelbase model and a long wheelbase model — also known by its acronym LWB. The extremely high collectible value of the car is also due to the limited production of only 50 units.

Ferrari 250 California LWB red, rear.
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The beating heart of the Ferrari 250 California was a 3.0-liter naturally-aspired V12, which produced some 240 hp. While one of the 50 models in good condition could be purchased for $12,500,000 in 2018, now the car's valuation has dropped to $9,300,000. The significant drop in the car's estimation, though, hasn't altered the timeless beauty of this Italian spider, and also, its overall high collectibility.