Totally depends on how much work you want done and to what standard. 1 day protection details usually vary from £150 to £400 for 8-10 hours work; 2 day minor corrections from £300 to £700 for 16-20 hours work, and 3 day + major corrections anything from £600 to well over a grand for anything from 24 to 40+ hours work. Detailer prices vary greatly with setup, experience and reputation. Like most trades really.