A friend of mine picked up a loose incomplete cybertron supreme Starscream and asked me how much it's worth. I've got a decent handle on vintage tf pricing, but not a clue on any of the aec guys. I told him I know who to ask though...
incomplete? not a whole lot. even complete one isn't worth much, i only paid $35 shipped 3 or 4 years ago.
Go to ebay and search for your figure in completed auctions. Take note of the condition - and average out the sold results. That should give you a decent current estimate.