SuperGrafx hardware has been cheap for many years now. Like most PCE hardware, the ones rotting on eBay are the ones people pass over, but they regularly show up on there at great prices.
Define cheap? I barely see a boxed unit go for under $200, then I look at the games and they range from $50-$500.
And also, yeah, it's not hard to get a great deal on one if you are patient, so even though it's pretty naff, it's still worth buying for cheap.
Guess I will have to be patient then. I wouldn't mind adding one to my collection, but I'm not spending big dollars on one.