If your going to buy the cartridges for Genesis, be prepared to pay for them...
The emulators are pretty good these days.
SF1&2 are both on Sonic's Ultimate Genesis Collection for PS3/360. I'm pretty sure they are also on Wii Virtual Console. Sonic's UGC is amazing by the way. It's a pretty comprehensive list of the best 1st/2nd party Genesis games:
Alex Kidd in the Enchanted Castle
Alien Storm
Altered Beast
Beyond Oasis
Bonanza Bros.
Columns
Comix Zone
Decap Attack
Dr. Robotnik's Mean Bean Machine
Dynamite Headdy
Ecco the Dolphin
Ecco: The Tides of Time
ESWAT: City Under Siege
Fatal Labyrinth
Flicky
Gain Ground
Golden Axe
Golden Axe II
Golden Axe III
Kid Chameleon
Phantasy Star II
Phantasy Star III: Generations of Doom
Phantasy Star IV: The End of the Millennium
Ristar
Shining Force
Shining Force II: Ancient Sealing
Shining in the Darkness
Shinobi III: Return of the Ninja Master
Sonic the Hedgehog
Sonic the Hedgehog 2
Sonic the Hedgehog 3
Sonic & Knuckles
Sonic 3D Blast
Sonic Spinball
Streets of Rage
Streets of Rage 2
Streets of Rage 3
Super Thunder Blade
Vectorman
Vectorman 2
Plus it has save states and trophies/achievements. And there are a handful of Master System games you can unlock.
Shining Force CD, though, is another matter. An emulator is probably your only option.