These days a lot of players in their early 20s are judged for their U21 performances. In that case, Delap is worth £10 million. I believe this is why Anthony Gordon was so expensive despite not doing much at Everton (although his fee was later justified).
That said, I personally don't believe Delap is worth anywhere near that amount and there's a big difference between U21s and real football. Due to his size it could also be that he could bully U21 players easily too which isn't the case in the championship. It still wouldn't surprise me if someone like Burnley went in for him regardless.