Rofl, Infinite Gold Bug:
1.) Build a tower
2.) Select a tower from the build-selection
3.) DON'T build it, but instead click on the already existing tower (still with the placing-square active)
4.) (placing square active, dont cancle it), click 2 time on the sell button of the first tower (first, the placing-square will disappear, than the gold amount will change to NaN = Infinite gold)
Bah, this is too easy.
First 3 lvls with Musket
Then buy the machinegun
Next the Flamer
And then the Raygun
Just upgrade some of the armor, so you dont get wasted by a few hits.
I think it's too much money you get. There should be less income.