Like pbj I'm always accumulating amazon points... for.... reasons, so I check amazon for vg swag from time to time. There are a few vendors selling the mega everdrive for around 40 bucks with a 8 gb sdcard. The ever drive 64 has also popped up for around the same price. It's very hard to get a cheap n64 flash cart, and again, I believe that also comes with the sd card, so that's also a deal to look after.
So for around 80 bucks that's master system, genesis, 32x (if you have the adaptor) and n64. Not too shabby!
I'm thinking of biting the bullet and ordering those two, but it'd pretty much wipe out all of my sweet sweet amazon credit.