Hi there,
I did my PPL at Billins about three years ago. Very friendly and informal although not as cheap as they used to be. Great fun flying the C150 (okay so its old but so what). They use GBTGP and GBOUJ for most of the training. I did my PPL over a few weeks in the summer and I would recommend doing it that way if you go to Billins. Weekends tend to be very busy whereas it might be you another guy and an instructor there on a weekday. The instruction is good in that you are likely to stick with the same guy. The actual instructors have changed quite a bit recently although I believe it has settled down now.
Cranfield is obviously a v good place to learn with a big runway and ATC.
I too did the rounds up there - Cabair weren't interested in small-fry wanting PPLs and I found Bonus (although very professional with nice offices etc) were a bit stuck up as well.
Regarding price - deals for paying the PPL cost up front are done.
Good Luck,
UJ