Tbh M ownership is fine, the main major costs that can spring on people (rare) are the valve shims not being done correctly leading to follower finger wear (my car has had this fixed), and a very few cars seem to have had big end bearing issues - mine was replaced preventatively. Either way - if you keep a few grand in the bank as a backup you'd be fine with pretty much all major issues. Theyre pretty reliable really.
Take the leap - the car finance world might be about to crash so interest in cars that are at cash-purchase price points could change dramatically.