An open top car always cost more than the hardtop equivalent except Porsche (Boxster vs Cayman). An extra 5-10% is what one will expected to pay extra for wind in the air motoring. Adding all the options up this Golf will cost £35000+. You might argue getting an A3 or 1 series cabriolet but their option will cost even more. However, I think the Golf will suffer savage depreciation compare with Beemer or cars with the Olympic rings as I still think the VW badge at this level will lose out more. For this reason, Im afraid my next new car wouldn't be a GTI with these prices! If I fancy a MK7 gti, it will be a used one!