I think a cheaper alternative if simply want to play Sonic 1-3 , unless you simply want the Sega Genesis for the aesthetics of owning one, is to get the
Sonic Mega Collection for the Gamecube or the PLUS version for PS2/XBOX in which they are pretty smooth ports. A quote from a dude from Gamespot says "if you're fiending for Sonic the Hedgehog and either don't have or are unwilling to drag out a dusty Genesis from the closet, don't hesitate to give it a shot." however another dude says "just blow the dust off the old Genesis, because there isn't enough good extra stuff here." You should check out if you're happy with the games on this where to buy one, I'd reckon Gamestop would own one although many Gamestops in my area do not sell GC games anymore.