Jenuis is right-try eBay. Watch current auctions, and pay NO ATTENTION to "BUY IT NOW's".
You are looking for AUCTIONS ONLY. Most "BUY IT NOWS" are WAY over priced and they sit. An item that sits is an item that does NOT sell because the seller wants TOO MUCH MONEY for it. It would throw off your assessment if you calculate overpriced stock into your equation. Generally, when I am trying to figure out a price, I look up 3 auctions (as Jenuis said, check out ended auctions, and watch current ones. Always wait until they sell), and do an average (add the total 3 selling prices, divide that number by 3).
Kicker773 is right. You can also ask around here. There is an AWFUL lot of kind, and smart Macross fans here who would be glad to assist. Help them out best you can by taking pictures.