EntirelyPets
EntirelyPets focuses on health products including prescriptions, vaccinations, and products like frontline and advantage. They say you will save 50%-70% off of pet store prices. They also guarantee that they have the lowest price compared to any US company, and will match the price if you find something lower elsewhere.

They do sell Baytril and a few other items forum users buy frequently, with prescription only.

Unlike some other prescription sites they guarantee to only sell FDA/EPA approved products.