Peterborough Conington or Sibson?
Either one fine by me although I have never been to Sibson and believe it can get waterlogged so we'll have to take the time of year in account.
Conington has no grass (
AFAIK) but a nice cafe and very friendly folk.
Cranfield is among the less cheap GA fields and not sure if they have all year grass but am sure that one of the locals can inform us.
FD