I think that US Apollo astronauts were on service pay - the typical rank was Colonel or Naval Captain and they probably got less than half what a long haul airline captain got. Then again they could retire after twenty years.
You could earn rather more from being an astronaut. I understand that at some stage during the Apollo (or It may have been the Gemini) programme astronauts shared the proceeds of a very lucrative contract with, I think, Time magazine. Many went on to front advertising campaigns (Armstrong Chrysler, Shepard beer, etc.)
I also saw that Buzz Aldrin was charging a five figure sum for a public speaking engagement around ten years ago. The trouble is that whilst the man in the street might be able to name the Apollo 11 astronauts, how many could name those who flew the later missions. I don't know how much Tim Peake could get as a public speaker but he won't be making a fortune as an Army major.