Plagatus wrote:
Consumability (disappearing forever upon usage) is the #1 reason why items are priced how they are. If you have an r99 Toy, only giving it to Illusen/Jhudora, or the applies-to-any-item loss through discard, gallery, feed to Skeith/Grarrl/Jetsam? etc. This would mainly apply to Food, Paintbrushes, Stamps, and the like.
Other things that affect it are special-giftedness. Pink Paintbrushes are worth more than they 'ought' to be because there is an avatar associated with Pink pets. Being non-consumable can drop prices on these things, such as Icy Snowflakes and Kasuki Lu cards. Books and r90-r100 Foods can be in here as well, as they are both consumable and potentially give trophies.
Attractiveness can greatly affect price -- Phnards, a high-rarity digusting petpet, are worth very little, while Baby Blus, a lower-rarity cute petpet, are worth much more.
Lastly, I believe rarity does not reflect rarity as a whole upon the site, but is merely comparable to other items that are stocked in the same shop. Say, perhaps every restock there's a 0.01% chance of an r99 stocking in each individual shop, but if one shop has only 1 r99, then that's guaranteed to be picked by the stocker program, but in a shop with 10 r99s, each one has only a 10% chance of being picked. I'm not sure whether this is right or not, though.
I tihnk the R99 items stock more often than that--else they would be worth millions, all of them. You also have to take into consideration LC and MP prizes, Treasure Maps (I got a really terrible R97 from one a few weeks ago, a Pirate Cannon if anyone's interested), and the like. Some items are also popular gallery items, such as dung-related items, Usukis, and plushies (especially the Neoquest ones).