PM "thenoname"
He had a GTM s/c kit fitted to a HR by Abbey Motorsport.
It's probs a little cheaper now, but when I priced up a TT kit in 2010, including all the supporting mods (custom exhaust, fuel return, re-map etc) and all the labour done by Abbey, the price came out at £16k. That would have given about 470bhp.
I know that's not the S/C kit, but it give you an idea of other options