Have you googled Prednisolone? I just looked it up and clicked on "shopping." Several online pet pharmacies popped up with prices as low as 15¢ per 5mg tablet.
Another option might be to call another vet. When there was a Prednisolone shortage in 2013 and the standard pharmacy price was $499...
If you're having trouble getting Prednisolone at a reasonable price, try calling another local vet.
My veterinarian was out of Prednisolone. I assumed other vets would be out of it too, but at a friend's suggestion, I did some calling and quickly found it in stock at another animal hospital...