There are auctions going for these all the time of ebay, the first of the trilogy is often going for 99 cents or 2 bucks, but then shipping is always around $7, sometimes as low as $4 tho. The other two regularly cost a little more, tho still only by a few dollars. The reason for the cheapness is just because there are so many of them out there, and probably a dozen SW snes games going for sale at any one time on ebay.
Here's a SW snes trilogy with manuals, ending in 6 hours, currently only at $16: http://cgi.ebay.com/Star-Wars-Trilogy-SNES-Lot-w-manuals-3-games_W0QQitemZ120123336602QQihZ002QQcategoryZ62053QQrdZ1QQcmdZViewItem
Here's a bundle of 46 snes games, all the SW ones included:http://cgi.ebay.com/46-snes-game-lot-best-lot-ever-includes-rare-games_W0QQitemZ200112143766QQihZ010QQcategoryZ62053QQrdZ1QQcmdZViewItem
The most I've seen is a bundle of something around 450 snes games going for about $400. The guy said he had been trying to collect them all... there are many large bundles that pop up for sale tho, I guess a lot of people have big collections.