Actually, I've seen them sell for between $1 to $1200($1500?) on eBay.
Many games are completely worthless. Then when some of the perceived to be rarer and sought after games are sold sealeed, sellers usually pick some ridiculous expontential pricce that they think thwey can get out of one person if they hold out long enough.
From what I've seen on eBay, sealed average games that aren't worthless of uber rare usually go for no more than double the regular price of a pretty good condition complrete copy.
If the game you're thinking of buying is Fatal Fury 2, don't pay more than $10 for it, but if you shop around you can get it for $5(and its best value you'll ever get for a sealed game if you intend to open and play it).