Agreed. I currently have a 6" bought off CL and it works just fine, however I too am trying to pick up an 8" if possible.I have a 6", and I'm on the hunt for an 8" at a good price. I'd love a 12" if I could afford it.
Honesty, buy the widest jointer you can afford. You'll be glad you did.
And it's true, a planer and a jointer work in tandem, you can't replace one with the other under normal circumstances.