I think its very hard these days to put a set price, or in same cases even an aproximate price on items. some simple little think that could have dropped 10+ items can sell for 100m+ while others are much less expensive, you may get 10 diffrent price checks on one item.
I do know that i paid 65m for a Shiv of Wrath about 2 years ago but i have no idea if that was a good price or not..
I see so many people, me including posting for price checks and they rarely get a reply, i guess one of the best ways is to maybe do a search on the forum for the item in question and see what others have sold for...again not always an accreate way to go as i think i remember a certain morter and pestle sell for like 2.5b lol. but anyways its a place so start. maybe someone else that is a collector of stolen items has a price for you.