the quote was up around a grand
Pete
As someone who has persevered and won with the valve block, don't give up! pop off to Ebay and buy yourself an 'O' ring kit, £28 or thereabounts. Also buy yourself the repair kit for the pump whilst you are there, the piston seal WILL be knackered. The motor in the pump is nearly bullet proof!
Now take out the valve block from the car, you've no worries about air pressure because you are on the bump stops! Once removed, and it is very straight forward, book yourself space on the kitchen table!
Renew ALL the 'O' rings and recondition the pump. 2 -3 full hours of coffee broken work will see you with a perfectly good pump and valve block, seriously! Take it easily and slowly, don't force anything. You will have all the tools bar the long allen key to remove the con rod off the pump shaft, and that is a Toolstation/Screwfix/Maplin purchase.
Put everything back into the car and off you go! Well you will need to reset the EAS faults, and assuming your airbags are serviceable, you will have a nice motor that goes up and down when you tell it and not when it feels like it!
I'll emphasis it really isn't difficult! Done mine and it is amazingly reliable. It does go down, but takes about a week to sink, but as soon as the engine is started it rises majestically in about 15 secs max often less!
Ian