Great game and to help some people i see in the comments here's some tips using the machine gun longer gives it a faster fire rate, boxes give $5 so getting something like $9435 is normal, wait until you get most the upgrade before playing elite, playing on easy gives no money, and i recommend using the machine gun then switching to the cannon mid fire then switch back to keep high fire rate on boss and good damage as the guns have separate cool downs.
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