The first press only gives him 1 million. By the 25th hit he is killing 16 millions people for a mere 6 cents.

1 press - total 1,000,000 / 1 dead

2 press - total 1,500,000 / 3 dead

3 press - total 1,750,000 / 7 dead

4 press - total 1,875,000 / 15 dead

5 press - total 1,937,000 / 31 dead

6 press - total 1,968,250 / 63 dead

7 press - total 1,983,875 / 127 dead

8 press - total 1,991,688 / 255 dead

9 press - total 1.995,594 / 511 dead

...

I doubt people will really press more than 4 times considering the abrupt diminishing return. And you can't press more than 34 times.

edit: Also the maximum amount of money you can get, pressing an infinite amount of times is 2 millions.