Found Trilogy at Rummage Sale

1965 copyright, First Ballantine Books Edition: October 1965.
Sixty-seventh Printing: November 1978

Got them for 25 cents per book. How much could they be worth to a collector? They don’t have the original sleeve, but all 3 books are in great condition.
I might also keep them since it’s been a long time since I’ve read the books and my kids got their hands on the old set I had.