Van Persie completed his controversial move to Old Trafford yesterday.
"We never thought we could get Van Persie," said Ferguson. "I thought Arsenal are not going to let him go. When I read he had refused a new contract that is when we acted.
"It has been a long haul and he (Wenger) got a great price - he could win a poker school in Govan.
"But we are happy the matter is concluded."
A cynic might suggest Ferguson went for Van Persie because, having celebrated his 70th birthday, the United boss simply does not have the time to wait for a new team to emerge as bona-fide challengers to Manchester City.
In Van Persie's case, the Red Devils are buying the finished article.
"He is what we have needed for the last couple of years," said Ferguson. "He has maturity in his game. His authority, timing and understanding of the game is complete.
"I hope we will benefit over the next four years."