Yes and no.
I do have the BTCC kit fitted on my car but it was part of the special edition run that Seat did with the Ref Sport. So I didn't actually have to buy the kit separately from the car. The car came with it all fitted.
Looking at the Seat Accessories catalogue it has the Aero Kit priced at £750 (this is without paint or fitting or VAT from what I can see) I also have the Seat Sport BBS alloys as well and I have the twin pipe exhausts as well which comes in at £250 (again with no fitting or VAT added)
So you are looking at £1000 for the kit alone and I would think the alloys would add another £500 on top of that. Then you factor in painting and fitting you could be spending at least £2-£2.5K.
Also I think I might have read on another thread that it might not be possible to fit the front bumper of Aero Kit onto a Cupra (assuming that you have a MkII Cupra) due to the washers on the Xenon lights.
I might be wrong but at least that gives you an idea.
Alex