I paid £480 for my GTX 980 and £550 for my GTX 980 Ti but £600 for the GTX 980 replacement/upgrade that is the GTX 1080. On that basis I would expect the GTX 1080 Ti to come in at around £720, possibly as much as £750 if NVIDIA release one of their (IMO) rip-off Founder's Edition variants first because they just drive the prices up. I was lucky to get my GTX 1080 FTW for £600 from Amazon, although I had to wait six weeks for it, as they currently sell for near £700 (at least they did last time I checked). I would not be surprised if the 1080 Ti ended up being £800. The lack of competition for NVIDIA means they can really charge anything they like as they know people will buy them. That's how they got away with selling the Titan X Pascal for £1,100 when previous Titan's have cost £850-£900.