If you don't have much money, I would recommend against a merc or a BMW as a toy. Their initial cost/performance is great, but parts really are expensive when they break, and even maintanence parts are significantly more expensive. I love Mercedes cars, my dad goes through a lot of cars just for fun, and the AMGs are the only ones he tends to keep a long time. He's had his current one for about 10 years now and it has treated him really well. But, as an example, his brake jobs can cost 4 digits pretty easily.

Then there's weight. I've been in some kind of racing most of my life, and I can pretty confidently say that lighter race cars tend to be cheaper to operate. Heavy fast cars burn through brakes more, break drivetrain and suspension components easier, use bigger and more expensive tires, need more power to go fast, and will travel further in the wrong direction when you lose control. So, depending on how tight your budget is, the more lightweight fun cars can be cheaper to play with.

If you're really tight on cash, it sounds counter productive, but sometimes just geting an actual race car is cheaper. Especially if you want to use it often. Lots of classes out there to have fun in Miatas, and there are even some inexpensive formula car classes. I haven't looked in a few years, but Formula 2000s used to be less than 20k for a pretty solid running car, and they're a ton of fun. There are quite a few classes in drag racing that dont cost too much either.

But I'm digressing, for street cars it sucks that we're in CA lol. There are lots of good options for fun cars though . Not sure what your budget is, but mustangs have pretty good cost/fun ratios. I still have a soft spot for the old 03-04 Cobras. Throw a pulley and a tune on one and they're a lot of fun. 4th gen catfish camaros with the LS1 are great too. If you can find a good C5 corvette with an LS6 they're even more fun. Evos are suuper fun to drive, I love they 8 and 9 but they're getting hard to find, and more expensive.

It's hard to recommend stuff without knowing your budget though. If you can afford something a bit newer like a 5.0 mustang, or something similar with low miles, then having a mostly stock, totally legal funmobile (maybe even with a warranty) might be the way to go. Lots of this is just personal preference though, so idk if any of this helped lol.