if you clear the room and have the radiator and valves ready for a plumber and you get it done in plastic pipe, it wont take him much longer than an hour, so guessing he'd use his own pipe, it shouldnt cost any more than 80 quid to him, pluss the radiator 55
total £135
this is if everything goes smoothly, their is a clear run for the pipes and the pipes that he could tap into are suitable