The Argentina striker has made an instant impact at Old Trafford with five goals in 17 appearances and Ferguson believes he has done more than enough to show he will be a sound investment.
"There is no question about his long-term future here," Ferguson told Setanta.
"David Gill (the club's chief executive) has spoken to his agent and told him we are very happy with him.
"The fee is in place. I won't tell you what it is but it is still cheap.
"I want to make this happen. He has impressed everyone with his appetite for the game.
"He'll get me 15 goals this season and what's more, they'll be important goals."