Google "tempe tyres" for better prices, especially for Kumhos.
KU31 is an excellent street tyre and I would buy it again (decided to try out other tyres). I'd say it's on par with Falken FK452 in terms of grip.
Longetivity, I had my KU31s last for over 20,000km, fronts were camber work but the rears went on for another 10,000km IIRC. Not bad on a heavy GT-R.
My old BNR34 wheels came with camber worn KU31s (approx 50%, unknown age), I drove around on them for about 10,000km and they were great, even in the wet. Had to change them because the insides were worn down to the belts hahaha.