He will probably go for closer to £60m but £50m is not an unreasonable bid. He wants to leave, he does not have a long contract. He’s 25 so he’s not going to improve significantly beyond the level he is at currently so is not comparable to the likes of Antony who have higher ceilings.
He has averaged 10 league goals a season for 3 years now, fewer than Rashford across that same period who is of a similar age. Spurs had a bid for Rashford rejected last week. Richarlison is the next obvious, available wide player with Premier League experience.
If he goes there, good luck to him. He has done well for the club and kept us in the league last season, he deserves Champions League Football and Spurs will give him that.