Inflation is an item by item thing. The retired items that will go up the most in price are the ones that get used up -- food (except Advent Calendar stuff which is so cheap that going to 500 NP is a huge jump) and books. I think books go up the most -- people trying for the trophy have to read as many as possible. But retired foods aren't gourmet, so they don't help with that trophy.

Me, I save 1 of everything -- that's my favorite thing to do on Neopets. And I LOVE Utility Fish. I wish they would create more of them.