must be fully trained and not just a pup. Surely you could buy a pup for way less after all training your own pup is most of the fun.look them up you'll see what they cost. All well bred gundog be it cockers, labs ,hpr's are all £700 + a pup. You can buy any bred for less but do your homework buy from tested parents. Yes you'll pay more but there's a lot bigger chance them making the grade. They'll be loads cheaper bred by people breeding them for money.
I paid £400 for my Lab off a bloke who trialled labs flat out. Her mother was a Field trial award winner but not a champion at the time.