This is something I've been meaning to do for my own purposes, but I finally forced myself to get them done to add to gameSniped.
Basically, it's a tool that shows all R6+ games for a given system listed on eBay, broken down by rarity level.
For myself, I find it makes it it easy to look for under priced games, or rare complete games.
I've completed them for two systems, NES and SNES.
I'm just announcing them to see if anyone else will find them useful. Also, If you'd like to see me add a certain system, just let me know and I'll bump it to the top of the priority list. Feedback is definitely appreciated.