I trained at EFG and can say they have some very good instructors. Biggin is a nice place to train but bear in mind it does get very busy at times and landing fees are quite steep at £22.10 for a C152 (last time I was there). I was advised to budget around £10k for training at Biggin but actually spent quite a bit more than that. So definately not the cheapest option. When it comes to payments I know EFG has a PPL package and you can pay up front for a discount or in 3 or 4 installments.
They have a website with prices
www.flyefg.co.uk.
Also if you're looking to fly weekdays I think Cabair has an off peak PPL package that may be slightly cheaper. Not sure about the other places at Biggin, but you'll be alright paying up front with both Cabair and EFG flying schools.