I don't know, anabel. If he's never been shown, or hasn't been shown in years, 3 - 5K seems reasonable. But if he has some legit recent test scores at Training or 1st, I would think 5 - 7K +?
What does a decent horse, confirmed on the aids, going Training/1st go for in your area? In my area, 5 - 10, then I'm subtracting for age and a little for correctness.
I'm also thinking that if I were shopping for a student or a client in that price range, I might prefer him over a just started young prospect, because of his being able to be ridden on the aids immediately and for his nice attitude and work ethic.