that is not a one time 50$ right, it is a total, so at the $50, $100, $150, ect. right?
The bonus is given for every $50 counted.
For example, donating $10 x 5 times will give the bonus on the 5'th donation.
Donating $5 x 10 times after that, will give another 250 ability points on the 10'th donation.
Upgrading to Gold for $20, then donating $35, will give bonus and count the remaining $5 towards next donations for the special bonus.