Most Medicines Vets prescribe are more likely than not something that is available to Humans, But has been approved and licensed for dogs, So marketed under a different name, Its this approval and license bit that costs the money, Take Tramadol, Vets will give dogs Tramadol to dogs whilst they are in there care for pain relief, But they are not allowed to give you a prescription for it to you as its has not been approved or licensed for dogs,
Most everyday vet prescriptions are available for a fraction of the cost if you are willing to look into it. In fact the old ways often work just