Heyo, LambdaDuck, thanks for the great feedback!!! (And sorry for the late response :P)
Increasing the cost of all upgrades was put there because in this way the player would not have bought only the least expensive upgrade mindlessly, but he would buy the upgrade that he thinks is the most useful to achieve the overflow, and it seemed like a good idea to me, but i understand your point, and the player's feedback recived showed me that it wasn't such a great idea after all, add on top of that the fact that the upgrades are REALLY unbalanced, and you get a game that is the complete opposite of a strategic game...
Well, this game was a great learning experience, and i'm glad I have made it...
Again, thanks for the feedback and thanks to have playied my game, it really means a lot to me... ^o^