Your looking at around 2½ grand (unfitted) for a DASC kit that's already imported. I did look into importing one myself awhile back but after you've taken shipping,VAT & import taxes into account there's not much saving to be made.
I've only found a couple of companies that do DASCs in the UK,
Torque Developments &
C.A auto tech if anyone knows of other places in the UK where these kits can be had,I'd also be interested - especially if they're less than 2.5k