First, thanks for the awesome script.
I have just a couple things I've noticed that I wanted to bring to your attention.
With the brand and price select menus, once a selection is made all other options no longer available. I'd like to request that a future release be altered so that you can make subsequent selections.
On a similar note.
The sort select menu does not pass the query string parameters from the brand and price menus. This means every time you drive into the desired brand and price range, any attempt to sort the results ends up delivering a wider range of products than expected.