At this point, I'm afraid your best option is to find a local vet, and the sooner the better. The weight loss, in particular, is troubling. I'd start with a stool sample to rule out parasites--probably not very expensive. A general blood test and blood chemistry profile would probably help a lot, and a urinalysis. It would at least help rule out things like kidney failure or diabetes. Of course, the more tests you do, the more it will cost. Maybe the vet will let you set up some sort of payment plan so that you can spread the costs out over more time?