I'm at Microcenter right now and all their used games are $.99
Everything is well picked over, but I got Luigis Mansion GC for $.99
Obviously stock(and maybe price) will be highly YMMV.
EDIT: and there were some marked $.49 and $.25(the latter being 50 bazillion copies of In the Movies for X360)
Oh, and if you find a used game not marked $.99 or less, have the price checked. The copy of Luigi's Mansion I picked up was marked $14.99