Probably the single best place to find the current selling price, actual value, what people are actually paying for an item is: ebay!
The trick is, do a search for "sold listings"
First do a regular search on ebay for the item in question..the search brings up current active auctions, items that haven't sold yet..those prices are meaningless, because people can ask anything they want, often far higher than realistic.
So instead, click on "sold listings"..That brings up auctions that have ended, items that are already sold..and it shows what people actually paid!
that's the useful bit..
yes, you might rarely find a sold item where someone still paid too much..but those are actually very rare. Often you will find several, 5 to 10 or more finished auctions for the same item..with those multiple sales, that gives you a realistic idea of the current going rate for anything..
Scot