I work for Porsche; we fit loads of brakes as these cars tend not to get driven much and the discs corrode. Take it for a proper run and they should clean up fine.
Your quote wasn't too bad, when brakes are changed, the list of parts is bigger than you think:
2 x Discs (around £100 ea depends if std/S)
1 x Pads (around £100 set)
4 x shims ( around £15 ea)
2 x sensors (around £20 ea)
1 x Fitting kit (£20)
4 x caliper bolts (£10 ish)
8 x countersunk disc bolts (not everywhere replaces these, pence each)
Add the £115 p/h labour and vat and it easily adds up.
We sell a lot of brakes over the counter as Euro/GSF prices aren't as good as before due to them buying on the continent and Euro V's £ etc
Tyres are fair enough, but they must all the the same "N" rating, if the car has "N0" and you can only get "N1" then Porsche recommend fitting a full set, must be matched for warranty.
P.S. was at Porsche Driving Experience last week at Silverstone, had the chance to compare a New

Porsche against the likes of M5,RS6,C63 AMG, Flying Spur, 7 Series and a few others, and it did include track time too.
New car is really really good.