If I was after an adult dog I'd say £150 for an entered dog is a snip mate. We always see posts from members asking for entered dogs but when ones comes up nobody buys???
Perhaps adding some more info on him may help find him a good working home,
Whats he like with stock, cats, kids, other dogs, is he quiet in kennels, jump, retrieve, recall etc.
Good luck selling him, I like the look of him