Also, you might consider increase the bonus reward on the Lvl20, as the 1mil will not be enough for the restart upgrade and to cash out some. Unless you don't plan to have your gamers replay.
Besides, can you provide us the total rewards per zone level? I noticed the reward is varied within each lvl of the zone.
Yes it is varied because it is sort of random which robots you will encounter through each zone (though I did make it more likely to encounter robots with same level -> zone) But then again, I find it nice to encounter lower leveled robots because you can get your reward faster (if you had upgraded your attacks)
Question: Why the cost is more than double for upgrading to attack lvl 6 for a merely 22 more damages? This will need zone 8, 9, even 10 to get the amount needs.