Looks like £170 is the going rate for a set of Ultegra 6800 Brifters currently? Using the pair that came with the Propel on the Emonda ALR so need to replace them before selling. Will keep an eye out for something used in good condition but they seem to hold value well.
Merlin have them for £170 w/o cables, same price on CRC with cables by the looks of things.
(10% CRC discount, 12% Wiggle and Quidco in my arsenal)
Keep an eye on Bikeradar's Classifieds. Just had a quick check and looks like some brand new Ultegra shifters sold on there for < £130 recently.