Liam
Signature or Greer Aviation. I've used both and highly recommend Greer.
If cost is an issue then driving is probably cheapest. If there is a few of you by the time you factor train fares from Dundee or wherever there ain't a lot in it.
I do agree that GA could be made more welcome. However on more than one occasion at EDI I have witnessed havoc caused by clowns either getting lost in the zone, on the ground, not knowing any Vfr routes etc etc. Frankly I don't blame them. It is a shame though. It's not the most operationally best laid out airport in the world, and someone taxiing at 4 kts while they try to work out where they're going can cause a lot of problems.