To find an exotic pet vet, try the following websites:
http://guinealynx.info/vetlist.html
http://www.rabbit.org/care/vets.html
http://homepage.mac.com/mattocks/morfz/PB_vets.html
These lists aren't complete, so if you don't have any luck with them, let me know where you live and I'll hopefully be able to find an exotic vet for you.
It's hard to know how much the treatment will cost, but I can tell you an office visit to my exotic vet is $66, and that is without any treatment. I live in a rather high priced area, plus I take my pets to a clinic where there are a number of exotic vets, there is someone there for emergencies 24/7, and they have all the diagnostic equipment needed so that they don't have to send you somewhere else for tests, and that tends to make their price a little higher. I'm guessing you won't pay more than that for the office visit itself.
It sounds like your frog has a bacterial infection, since many other bacterial infections in frogs manifest themselves as bubble-like lumps or swellings. If this is the case, you will have only the cost of the antibiotic, in addition to the office visit, to pay for.
Let me know if I can be of anymore help.
