lovetyres.com are often cheapest by miles for tyres
That said, i wouldn't be buying FK452's. One of the most overrated tyres in history, mostly from owners forums saying how good they are because they're cheap.
The Vredstein Ultrac Sessanta is meant to be better. And tbh, i think the proper good stuff like the Goodyear F1A2's are only a few quid more expensive per tyre.