I cannot claim to have type specific knowledge (I own a TB20) but the problem isn't borrowing 10k for a C150, as a personal loan which will always be ultimately recoverable from the borrower personally (even if the small print doesn't say so).
The problem is that it might cost you 8k on the first Annual, and you might get a bit p*ssed off by then, but you still have to pay back that 10k, and unless you spend the 8k on the repairs the plane is worthless
These old wrecks have a value which is basically the time left on the engine - same as old piston twins really.
A certified engineer can pick up an old dog, repair it and get it flying by the application of a lot of his own time, signing off the work as he goes. Then he can end up with a nice cheap plane. There is nothing actually wrong with a C150 - it flies very nicely. Slowly
But for a non-engineering non-hands-on relative novice owner (apologies if I got this description wrong) looking for a cheap runaround which will last him a few years and then be dumped, forget it. You can do that with cars (well you could in the days when you could buy a dodgy MOT for £25) but not with planes. Well you can do it in Botswana but not in the UK