If you have Costco membership they do Michelin PS4 in 17's for about £91 fully fitted with nitrogen fill but they are running an offer where if you buy 2 tyres you get £20 vouchers and £50 for 4 hence why I got mine fitted there recently.
If you don't have Costco membership I find F1 Autocentres quite competitive, they are going about £88 fully fitted for the PS4's (or about £85 if you use "COMPA2015" voucher code).