Yeah, it's a biggy! There are TPB versions too that are much cheaper, but finding a first edition hardcover with the dust jacket is near impossible, and the price is outrageous. Reprints many stories featuring the main female characters from the Marvel Universe. If you can think of one, she's in there. At least up to '77 when it was produced.
I think back then the artists and writers were paid to do the job, and once paid, Marvel owned the stories so they could do whatever they wanted with them. Dynamite owns Red Sonja now, and they have reprinted all of the old stories in the, "Classic Red Sonja Remastered" books. Issue #50 even reprints Red Sonja #1. I doubt they paid the artists and writers once they paid Marvel for the rights to publish, but Maroto, Romita and Brunner have done covers for Dynamite's Red Sonja books. So while they may not be getting royalties for their previous Marvel work, at least Dynamite had respect enough to have them do some amazing covers for the newer series.