Hi! Yeah, I was thinking the same thing. Since you have 20 barbed wires, you should be able to complete it with less money. I'll tweak those numbers.
They don't make much of a difference in the demo, since you can probably beat it with survivors and a strong mouse, but after those 15 waves (the easier ones), the full game has more waves and stronger bosses, so you'll need all the help you can get :-)
Thanks for playing!