Anybody buying Kaka for more than 20 million euros is insane.. He was a GREAT player, but he WAS a great player. Ronadinho was better than him both at their prime, still when you lose your form AND health AND your 29, the chances that you are gonna be VERY good again aren't great.
The best option for any top club will still be NOT buying him, when there are tens of other players who can give you more in the midfield than what Kaka is most likely gonna be able to give..
Glad to see United's name missing in the list of the clubs who are interested.