Torah Temimah (10, citing Megilah 14a): A parable for this is two men. Ploni had a mound, and Almoni had a ditch. Almoni longed to buy the mound to fill in his ditch)! Ploni longed to buy the ditch (to get rid of his mound. When they met, Almoni asked to buy the mound. Ploni said 'if only you would take it (for free)!'

Malbim: He was happy to pay for the cost of fixing the nation's conduct.

Vilna Gaon: Haman did not mention which nation, and exactly what he wants to do to them. Achashverosh authorized him to do whatever he wants, to any nation.

Malbim: Do as you see proper to fix the nation's conduct.