My cat has ringworm, what should I do?

I am almost 100% certain that my cat has ringworm. I've had cats before and know what it looks like (and I've had it before). An office call to my vet is $50, and I really don't have money right now. I have other cats and don't want them to catch it. The vet hasn't seen this cat yet because he is new to the family and I had him fixed at the shelter (just a week ago). Can they write me a prescription for it without seeing him or is this going to me another monstrous vet bill?