I just picked up 2 very similar to this (no turbo buttons) for $13 a piece from ebay (new). Downloaded ZSNES and I've been playing MegaMan X, F-Zero,Sunset Riders, SF2 and UMK3 like crazy!
Watch where you buy from though because there is a very high fluctuation in price and quality. If you have some original SNES controllers you're better off just buying the USB adapters. They're the same price but you get the authentic experience of using a real SNES controller.