I just noticed a large bump on my 18-year-old cat's back leg/paw. It isn't there on the other paw. It matches his skin color, and it's not particularly hard or soft - about the same texture as his skin. I haven't seen it before, but I haven't looked closely at his legs in several weeks or so. My mother controls both the car and the money in our house (I'm a full-time student, no part time job) and she is extremely averse to taking him to the vet unless it's absolutely necessary, for financial reasons. Any ideas on what it might be? If it looks bad, I'll at least have something to tell her to convince her to take him to the vet. (I've included pictures)