I wrote a long piece of text which disappeared because of a connection fault, so I'll make this concise.
Prices of items are not raised to increase an item's value because the lower the prices are, more likely people are to buy them from torishop. The current prices have been found to be quite effective and there aren't really staff in toribash who would actively monitor what prices players are willing to pay for individual items, so no item prices are raised. The prices must be suitable in the sense that people want to buy items from torishop by which tc goes to toribot which is an account from which tc can be deleted and therefore tc's value raised, and furthermore people have to buy more tc with real money
^no facts here, just guessing with logic