BMW successfully manufactured the RWD E36 3-Series from 1990-2000, and it has enjoyed a resurgence in popularity over the past ten years. The top-of-the-line M3 has an almost cult-like following these days, as seen with the late Paul Walker's car collection. People truly bought into BMW's slogan of it being 'The Ultimate Driving Machine'.
Originally the MSRP ranged between $21-$40K, which is $42-$70K in today's money. You would expect a well-engineered and high-performance European car to be moderately expensive to maintain, and it is. We've seen that as a brand, BMW ranks near the bottom for reliability, and near the top for most expensive average maintenance/repair costs. If you intend to own a 20-30-year-old European car and are not independently wealthy, it's best if you're an avid DIY'er with time on your hands.
According to most resources, there are four specific issues with the E36 that must be addressed sooner than later. Let's see how much the cost of those can be.
Coolant System
If not properly maintained, leaks in the coolant system can and will lead to engine overheating, which leads to blown head gaskets and engine rebuilds. There are apparently a lot of cheap plastic components, so it's recommended to rebuild the entire system every 70-80K miles as preventative maintenance. Consider replacing the radiator, thermostat, sensors, hoses, and belts, as well as the water pump which has a cheap plastic impeller that cracks and sends plastic shards through the cooling system. You should search out quality aftermarket parts rather than genuine OEM, as they're often much cheaper and actually perform better. Aftermarket parts can be had for approximately $400.00, and a competent DIY'er can do the job in four to eight hours.
Suspension
Not so surprisingly for a 20-30-year-old vehicle, the suspension needs to be addressed next. Overall, BMW's are known for their stout and stiff suspensions, but key components like bushings, bearings, and mounts are notoriously bad. The worst-case scenario means you would have to consider buying an entire front and rear refresh kit, which includes tie-rods, sway bar links, bushings, ball joints, control arms, shocks, struts, and also engine and transmission mounts. BMW owners swear that these changes/upgrades breathe new life into their old cars but be aware it could cost you $2500.00 in parts. Not to mention you need special tools and specific skills if you want to do the approximately sixteen hours labor yourself.
Vanos System
In case you didn't know, Vanos is the special name BMW gave to their variable valve timing unit, which is responsible for controlling torque and mileage. If the Vanos piston isn't functioning correctly, or the cheap plastic seal is cracked and leaking, you could noticeably lose power in the low end, get much worse gas mileage, and hear what's referred to as the 'marble in a tin cup' sound. Prices range from $50.00 for just the gaskets and seals to $500.00 for the whole unit. Unfortunately, an experienced mechanic has to handle this job, as special tools and engine timing adjustments are needed.
Finally, these engines tend to burn an excessive amount of oil. Apparently 0.5-2.5 quarts of oil every 2K miles is considered normal. If you're lucky you can just replace the head cover gasket for under $200.00 with labor, and/or the CVV (crankcase vent valve) for under $200.00 as well. If the piston rings are leaking, consider buying a different car.