If ever a price reduction was needed, then I'd say this; 20% off all ranks. This would mean;
- Iron donor is $8. This is rather an odd price, so perhaps we leave Iron as $10. Gives more incentive to buy a higher rank, with Iron's relatively low 'bang for your buck'.
- Gold donor is $20. This may not be so much off the now current price of $25, but again, it offers incentive to possible buyers looking for a more value for money option.
- Diamond donor is $60. This is a bit more affordable, but it's not exactly great value for what it is, given Platinum outdoes it in several aspects of perks and rewards.
- Finally, Platinum donor is $80. This is the current price of Diamond plus $5, which has since been superseded by the Platinum rank's introduction. A little more affordable than the usual $100 fee which deters some from purchasing it.
Logically, premium upgrades from Diamond to Platinum are now $20.
My 2c (haha get it, we're talking about money, and... okay, I should stop).