DC collected the entire thing in hardcovers. Most of them are out of print now, but they can be found for 20 bucks or so a piece. They get really good at vol 13
(which is 80 bucks now but most of them are a lot less). Volumes 1-6 are the early stuff and are really good. Volumes 7-12 are when Eisner was fighting in WW2 and suck and everything after that is when the book was in it's golden age. DC also did a Best of the Spirit paperback
but I don't have it so I can't comment on the reproduction quality or what stories are in it.
Byrne's best Fantastic Four issues are 242-262. Those are the classics.