Like Joose siad it's all about if you want the originals or not. But here's what I know as far as the Indy comic history.
In 1981 Marvel did a 3 issue series addaption of Raiders. Then later that year they released 1 Raiders comic book that collected all 3 stories (my personal fvorite piece in my collection)
Then in 1982 (pretty sure) Marvel started a series of Indy comics called "The Further Adventures of Indiana Jones" This ran for 26 comics (correct me if I'm wrong there) with 12 comics per year.
In 1984 they released a 3 comic adaption series for Temple of Doom and later on 1 comic that collected all three issues into one.
In 1989 Marvel made their last Indy comics with a 4 issue adaption of the last crusade. I remember hearing that these issues had variant covers but I may be wrong. Then later they released them all in one comic.
Now Dark Horse comics dd a few Indy adventures such as one of my favorites "Thunder in the Orient" and an adaption of the video game: "Fate of Atlantis" I don't remember the other series' of the top of my head.
Dark Horse also did 12 issues of the Young Indiana Jones Chronicles. I believe that the first issue has a few variant covers or something like that.
In 2008 Dark Horse did a 2 comic adaption (each with variant covers) of Kingdom of the Crystal Skull. And they did a story called "Tomb of the Gods"
Joose told you about the omnibus books
So that's pretty much the history that I know off the top of my head. As for prices: I got all of my Further Adventures books for about $2 a piece (but check ebay sometimes they have the entire lot for a good price) I got the young Indy's for around the same price as well as the movie adaptions. The 2008 dark horse comics were $6 per KOTCS comic and I think $4 for each tomb of the gods comic. THe omnibus' run at about $25
So that concludes my longest post yet.