I was poking around the CAA website trying to find examiner fees a while back and i saw a huge charge for the initiation of GPS approaches, i think it was around 8k, cant find it now but on the previous points, to upgrade to Full ATC is a minimum cost of £10,450 to the CAA plus for a small airfield (say up to 5 ATCO's) you pay £3635. These are just CAA charges, not including the cost to the airfield for training etc.
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ORS5 No. 242: Aerodrome Licensing and Aerodrome Air Traffic Services Regulation | Publications | CAA
Im sure there are alot more charges hiding in the system but when you have to pay this amount up front is it really worth it. To the pilots yes, to the guys paying the bills no. There should be an easier way to pull small airports kicking and screaming into the 20th century without making them go bust for the pleasure. (in a sense rather than forcing them!!)
DBB