I've seen some in fair to good shape range from 600-1500 u.s. dollars
You're smoking crack. A Q-bert with under 2000 plays went for $1600 a little while back. That is FAR above "fair to good" shape. We are talking near MINT.
Just 2 days ago another NEAR MINT one sold on Ebay for $910.
http://cgi.ebay.com/Qbert-Q-bert-Arcade-Video-Game-Near-Mint_W0QQitemZ6222236701QQcategoryZ13716QQrdZ1QQcmdZViewItemThe days of $1500 "common" classics are over. The market is dead. People who want certain games either already have them or would rather put their money in a mulitgame. I went to a Superauctions about a month ago and I don't think one classic went for over $600. Two Star Wars uprights went for $500 each. Those things used to bring $1500. Meanwhile, one guy brought like 10 Multigame cocktails to sell. Each of them sold for $1700-$2200. Cha-Ching.
The best way to figure values is to check the Ebay completed auctions. A Q-Bert in good, solid condition is $400-$600. As for "fair to good", $300 tops.
Peace.