get yourself a job marshalling. the pay is reasonable (£3.50 ish per hour) and usually the owners will let you use the fields after the day is over, and you should be able to borrow site kit.
buying a marker isn't so expensive once you start earning £25 per week, in about 2 months you could buy a very nice shocker + all the kit (they are SUCH good value for money second hand!!!!)
that should start you off in the world of paintball. and stay on here, it is the best place in the world for paintball advice and to keep you up to date on what is going on!!