Not at all mate, you'll be very surprised at the price of range rover spares.
Datatek above makes cables to diagnose this sort of thing. Its so easy to use even the missus has reset ours when its had a moment! I would highly recommend getting one so at least you can post up fault codes etc and reset your own suspension.
I would also look for a landrover specialist as the dealers can get very pricey if you feel you can't tackle it yourself. A rebuild kit for you compressor is dirt cheap on ebay so don't worry just yet. I rebuilt my own and the kit was £20 or £30 if I remember and the bags cost me £60 a corner. I did all four for peace of mind as has been already mentioned they have a certain shelf life.
As wammers said you or your mechanic need to find the leak, very easy with a bottle of spray soapy water. Could be a bag, could just be one of the air lines. At the top of the page is a test to check your compressor as well to help ease your mind.
If you took the whole system off the car you'd be surprised how simple it all is really. Keep the faith and you'll be fine.