I seem to recall that the pay wasn't too bad. I think FO started out at around about top Flt Lt money. In my short time in Civvy aviation I've come across plenty of people who've taken pay cuts to do a job they fancy. I currently regularly work with a guy who gave up foreign contracting on big money to take up a part time job just so he could live in a particular area of the country. It's not all about the money.
I have no idea about the background of any of these guys but what's not to say they haven't come from from Far or Mid East contracts, with bank accounts awash with money and now fancy flying with the RAF, something they perhaps missed out on earlier in life (caveat - I have no actual idea)? Or they're living in Oxon and are sick of driving to MAN or LGW?