August 2nd, 2002, 10:28 AM
It's not sci-fi specific, but I've gotten good deals from the Quality Paperback Club (qpb.com, you can do almost everything online if you want). They sell mostly paperbacks and often get exclusive contracts to issue paperback editions of books when everyone else only has hardback. You can also quit almost immediately--they don't have crazy requirements to fulfill.
When they carry sf, it's usually classic stuff, like I just ordered a 3-in-1 volume of H.G. Wells. Still a pretty good deal and almost always beats Amazon pricing.