sleepy, I just did a little googling and playing around.
If you go to the "audible audiobooks & more" section on Amazon:
http://www.amazon.com/b/ref=sa_menu_...ode=2402172011
Then click a category you're interested in (say nonfiction). You'll get a huge address in your browser address bar.
Go to the very end of that address and add the following:
"&field-price=300-499&redirect=true"
where the two numbers are the price range (in pennies) that you are looking for.
I'm sure there's an easier way, but this does seem to work. Here's an example with "fiction and literature"
http://www.amazon.com/b/ref=amb_link...&redirect=true
the nice thing about it is you can sort these results by "new and popular" etc instead of just wading through a bunch of crap strictly sorted by price