Item balance is something I discussed with another modder before, and we both came to the conclusion that it is utterly pointless to try and balance the items when the core difficulty is so low. I've toyed with making some items really costly, but all that did was make me ignore them. You don't need items to get gamebreaking income levels, so why bother with them unless they're really cost effective? The best you can do is design your own item balance to suit your need and not worry about it. It is impossible to lose a game of WM in its current state, so just customize your item list for personal preference.
Having an additional tier of catacomb rarity would be nice though.