You probably don't want a Supergrafx. I've been collecting PCE since the system was in its prime, and I still don't have one (even though I own multiple PCEs). They don't play CDs unless you buy an add-on CD, and the only feature they have over a standard HuCard-only PC Engine is that they can play Supergrafx HuCards, of which there are only a half dozen, and none are impressive, IMO. Its more of a collectors thing, really.
If you want a reliable system, your probably want a PC Engine Duo R, or Duo RX. Conventional wisdom says that original PC Engine Duos are less reliable, but I'm not sure how true that is. They are all year or three newer though, that much is known, so that might work for you.