Visited Denham yesterday as I am looking for some flying close to Islington.
Cabair have expensive rates and will not pay for any landing fee's, plus they have fuel surcharges.
The Pilot centre across the airfield (aside from having an amazing cafe next door to it) has a decent set of rates with a good fleet of 152's 182's and PA28's. All their prices include VAT, landing fees and insurance. Their membership is also good value.