I wouldn't finance a racecar if that's what you're thinking about doing, that would be... very silly.

A big wreck that wads up a whole car would take me out for a season or more but it's not the end of the world. I'll probably always be racing go karts too after all. I don't own cars for the street I can't afford to eat the cost of either, not a fan of high insurance premiums when that money could be spent on race fuel and slicks.
Spec miatas aren't really any cheaper to buy or total than an older pinto-powered FC. Running costs are cheaper though, they're a lot more rugged and reliable, there are more places to race them, and you sure as hell won't be lacking for racing competition or community. Definitely a lot of appealing things about them. I raced a loaner last weekend and it was pretty fun, they're a pleasure to drive. I've just got too many stars in my eyes for cars with no roof and big wings that go super fast.