The wiki usually says where items can be found, whether its on the description or if someones left a comment. As for general prices of items, they are always changing, things are more expensive at the start of a ladder reset, patches change causing items and builds to change. I dont think there really is a fixed price on items, but, the best thing you can probably do to figure out prices is to look on the trade section of the forum or go the the trade chat on the anni discord someone will help. As for your items, i would hold on to them for now. A new patch is coming out soon meaning they could largely increase (or decrease) in value, wait till the dust settles i guess...