Thanks for the info IceColdFever, time to load up my store and test it out.
Edit: Okay, the new page basically splits the reprice fields in to 100 items, so the first 100 items have the form fields price0 and limit0, the next 100 are price1, limit1, etc. This shouldn't be too hard to fix.
Something else that came up is that I noticed when you have a lot of items in the store the store inventory request takes a really really long time (potentially manifesting itself as a "freeze" for impatient folk), I am guessing this is due to the lookahead in the matcher, so I'll try to fix that too.
Edit 2: Here's the patch. The previous issue I had of not being able to reprice certain things was due to me telling KoLmafia not to price things at minimum sell price, d'oh! This patch updates the store manager to use the new behaviour of splitting reprice requests per 100 items. I also optimized the way manageprices.php was being parsed so now the frame should load noticeably faster when you have a bunch of stuff in your store (ie. >100 items), but it's also faster generally.