Well like I said, get an everdrive md. The Chinese versions you see on some websites are identical to the "official" one and you will pay about half.
So long as you don't care about the condition, you can get a working genesis for around 30 dollars. Just make sure you get a model 1. It has stereo sound (via the headphone jack) and is littered with hardware glitches. That sounds like a bad thing but these glitches were taken advantage of by various game companies to make new sounds and visual effects. So on a model 3, for example, gargoyles doesn't play right and the sound tracks on several games are "weird".
It's a good investment though. Get a model 1 and the everdrive md and right off the bat you can play all the genesis games and most of the master system games (if you get a master system gamepad I believe you can play them all). Buy a 32x adaptor and you can play all the 32x games as well. If you get the sega cd add-on you can boot different bioses.