I'm not quite sure if I understand what you precisely mean here. The problem is not with other clubs, showing interest in Mitoma. There are plenty of clubs queuing up for his signature. The problem is with Brighton that does not want to sell.
You can't pluck a figure of 80m for Mitoma out of thin air based on the rumoured asking price for Paquetta, Caicedo, etc.
No more than I can use Brighton selling Trossard for 25m or us buying Kovacic for 30m as a 'benchmark'. Different players.
He is a player with only half a season of note, at the age of 26. His price will reflect that.
But if you really want a benchmark, we flat out refused to offer Brighton more than 30m for a much more established younger player with twice as long left on his contract just last year,for a position we at that point really needed to fill. Maybe start there.