Oh, I don't know...
...a friend of ours is in the horse racing business and says that veterinarians can prescribe some of the same medicines that human doctors can, so maybe going to a vet for a prescription might not be so bad? I'm pretty sure one's insurance wouldn't pay for it, but what do I know? I don't go to a vet.
Many of those drugs are available without a scrip from the vet supply store, sometimes cheaper than even the copay from the pharmacy. You may have to do a little math to get the right dosage (different weight pills), but they're generally made in the same factory to the same standards.