My opinion is that your a little late for buying Captain Marvel #25 to 33 as those books have already shot up in price. Marvel-Two-In-One Annual #2 is also going crazy. The Warlock books are JUST starting to go bananas but I think that's just because they are hard to find in HG and people recognize how awesome they are 40 some years later.
Luckily I have 3 HG copies of 25 and 1 HG 33. There are still some good deals to be had though on the other issues in Starlin's run. Marvel Graphic Novel #1: The Death of Captain Marvel is another important book for anyone looking for Starlin's Thanos Saga. I am trying to get a Two-in-One Annual #2, but yeah, they are steep. These are great books that I first discovered over twenty years ago when I began collecting comics. They were very monetarily undervalued, but that has changed.