So I'm not up on prices at all, but believe the adage "if it sounds too good to be true, it probably isn't."
I'm curious why someone with a car in good shape, so amazing, would want to get rid of it after only 6 months...unless it was just to make money, in which case I'd worry about issues seen or hidden.
Subframe is sure a big issue...but so could an overheat...so could be a suspension so raped that you need an entire new one. SC isn't just tough on a motor, but tough on the entire car...if used properly, that is! LOL
...and then there's your price range. If you have one, I'd say you should probably deduct about $2-4,000 for things you might need in the first year. Maybe more.
If you want a bmw really badly, wait for an ordinary, unraped car from some old person like me. I'm selling mine for $37,000 if you're interested.