Rats do not do well by themselves, even if you give them lots of attention. They need other rats to play with, so you'll need to get a pair of females, not just one.
Also, you likely won't find someone who will just give up their cage for you. Martin's Cages sells good quality cages cheap, or at least cheap considering all the other things you'll need to buy to properly care for a pair of rats, including vet bills.
www.martinscages.com