If you are not mechanically minded I would consider taking your car to someone like Dave Andrews for Vernier fitting I think he quotes about £300 to supply and fit.
What ECU does your car have, is it an MBE?
I've not had it done but IIRC Steve G charges about £400 for a mapping session.
Best speak to both of them directly for more accurate figures though
Bozz
McLaren Orange and Black 1.6SS 6 Speed here