A respected transfer-market source said: "United effectively ran out of money in the summer in terms of their budget for signings.
"They wanted Baines but couldn't afford him after paying £22million for Van Persie.
"But that deal was too good to miss and Fergie has been proved right in pushing out the boat for RVP."
United are not the only big club who would like to sign the ex-Wigan man. Liverpool have a long-standing interest but that would be a tricky move for Baines.
But Baines says he would prefer to continue in the Premier League, rather than move to Germany.