It will cost you about £1100 - £1200 for the actual diff ready to install in your car, the quaife atb unit is £805 inc vat, then you need to have it fitted in your existing diff casing, new bearings, labour, shot peen + polish the cwp etc etc. Well worth it though, get the quaife built now before you waste money on a 2nd hand std diff (which will break, just like the 1st one)