I've recently done mine at RAF Cranwell. Total cost £60 (two cheques) which includes the MO's fee and an ECG (that is required to be sent to be sent to the CAA). The best bit however is that the MO has access your CAA details via your ref number, such you can receive your signed Class One there and then. If you are travelling to Cranwell-Top tip, do all of your pre-med george (bloods etc) with your local sickbay before you book in and then self carry your med docs, thus you'll only be with the MO for 30 mins ish.
Other places-RAF Benson, High Wycombe and RNAS Yeovilton (not sure whether the MO is still at Yeovs now though)