I tried messing around too. I tried simply using only 1 technology to beat the game. First was the green technology, which I only tried once so far, but I was unsuccessful. Then I tried the blue technology, and again was unsuccessful due to the cost and not being able to take out the bosses for the extra money - again, only tried once, but failed. Finally the red turrets, which I knew would win easily, and it did. The range and cost is very efficient, even on the yard sale at the end!