When you have patch 1.2 installed it's easy to get more money:
Go in the buildmode. There you buy any object and place it at a spot where you can't
place it (object will be shown transparent). Then you click a few times at this spot
(object will not be bought). After that you place the object somewhere where you can place it
and buy it. Now use the undo function of the game. The object is gone but when you click
again on undo you nonetheless get the money for the object.