Yep, White Waltham is a lovely place to fly - but definately not the cheapest.
Don't forget that whatever rate you get for 'block booking' there are membership fees and fuel surcharges to apply as well. Check what you're paying.
There were plenty of sub £2000 PA28 shares on the board this morning. Problem is with such large groups is availability - some of the 20 or so members may get a bit arsey!