Why is Dr. Heinz Doofenshmirtz so rich.. I mean where does he get money from all his inventions? Did he invent moneynator?

Well in the episode where Isabella gets cold and Dr. Doof decides to make another inator unfortunately I don't remember names since it's been quiet while I haven't watched the old episodes. We see Doof's wife saying that she'd stop giving him money for his foolish inventions in the end because of the switch of the blueprints Doof's invention was gone to the brothers and Doof's daughter was unable to get him caught.

So most probably he gets his money from his wife.