Try looking not in a pet store, but in a feed store or farm supply store. Some carry supplies for small animals as well as farm animals. Also, ask your vet. If they don't carry what you are looking for, maybe they can suggest where to look. Can you post your question on your local Craigslist? Do you have a shelter or rescue nearby whom you could ask?
For good Timothy hay (adults want Timothy; pregnant mommies and babies want Alfalfa) at a reasonable price, ask someone who keeps horses, llamas, alpacas, or other large animals. They need so much of it, they would never pay the prices that small animal owners pay. Even if they don't do pure Timothy, they should be able to point you in the right direction. I get my Timothy (good fresh stuff, too) directly from a farmer, by the lawn and leaf bag full, for free
. Okay, so I married a farmer's brother, but still, if you ask around, you'll find a local, inexpensive source.
Good luck!