I generally use eBay as a guide and don't assign concrete values to my items since people use that to try and trade me a few newer/common items for most valuable/rare items, ie, I'll trade you two new release games for Xenoblade (which they think is justified because the new games have retail price of $60 each). If really want numbers, I'd probably say $100-115 each.
You can check my wantlist to see all of my wants but as I said, I'm not going to trade either for a bunch of new/common games.