I had 418 Gold.
I buyed 1 pickaxe upgrade.
Now i have 58 Gold left.
So it cost me 360 Gold instead of the 120 Gold like indicated on the buy button.
And BTW, i have Pickaxe to level 2... Now i'm mining 3,16 Gold per 5 minutes instead of 5.
Could you please revert me to level 0, it was more profitable then level 2.