Unfortunately, rust free in cars this old means that someone has cut it out. To then have it back together and running, you're looking at significantly more than 10 just for the work.
10k will buy you a 240, but it'll be a long way from pretty. 25 will probably get you a running, good nic (not much rust) 240, but even then it won't be rust free.
Could get a nice project 2+2 for 10