I don't know if it's a state or federal law, but here in Indiana, it's illegal to prescribe medication if we haven't seen the pet in over a year. Has to do with having a "client-doctor" relationship.

A flat white worm could be any number of worms,; tapes are just one of many it could be. Roundworm and pinworm are two possibilities that immediately come to mind, and not all dewormers treat all worms. The vet will also need an exact weight (in grams) to calculate the proper dose. I would be extremely suspicious of a vet who recommended using something over the counter without diagnosing the correct parasite. A vet who would do that would make me think they don't really know anything about snakes and could possibly tell you to use something that could kill your snake.

At our clinic, a fecal only costs $15 for a flotation and smear (you could probably ask them to just do a float if you have a larger sample, at least a teaspoon size or so), and exotic exam costs about $50. Medication charge will be dependent on the type of med, but if it happens to be a worm that can be treated with something OTC like Panacur, let them know and they'll just tell you the dose to use.