A short service Commission for aircrew is 12 years, 6 years for ground branches. If you go in as aircrew there will be a return of service period, not the full 12 years, but perhaps 8, you'd need to check that.
Clearly 8 years or so as an RAF Pilot would have the airlines snapping at your heals once you left. I would also think that any time in the RAF, even in a ground branch would make you more employable in the civilian aviation industry. You will have much experience working with and around aircraft, Flight Operations, will probably have operated in harsher conditions that most on operational deployments to the Middle East, you will have made decisions that most don't have to and will probably have good management and leadership experience that few get in their 20s.
So, if you can't afford civilian flying now and want to do something interesting for the next few years its worth looking into. Also, there are a number of RAF flying clubs that service people can use at a greatly reduced cost. Akrotiri for example is around £50/hr. At 24 you are on the limit for aircrew, but plenty of people have got in slightly older.
I wish you well with whatever you choose to do.