^What Knuckle Duster said. Here's my prerogative:
Indeed, the DC's are a dime in a dozen. It may have died-out too early, but it sold a helluvalot of units. You won't find as many Saturns though. Both will run you the trouble of having to fix that laser eventually, but if it's around the same price (as it sounds), then the Saturn it is.
You won't find that many (or as many) in the wild. Also, here's another more important point, Dreamcasts or Saturns (but especially Dreamcasts) shouldn't cost you more than 20 dollars, complete. But I guess we're talking about more than 20 dollars here, so if you were going to spend more than that, then spend it on a Saturn. Again, the DC's are a dime a dozen (and that's not me saying it's the right cost, it's just that it is terribly underappreciated. But then again, so is the Saturn).
By the way, the Saturns have started to pick-up their price range, so go for it if it's low enough.

