Tiered Bonus Structure

I need to present dollar values to my boss for a proposed tiered bonus structure and am trying to figure out how to create the necessary formula.

The bonus structure is as follows:
Level 1 $8,500 = 3% of fees up to $8,500
Level 2 $10,500 = 5% of fees between $8,501 and $10,500
Level 3 $15,000 = 7% of fees between $10,500 and $15,000

Tricky part is bonus amounts do not go back to dollar zero. The percentages are only for the stated range.

EX: Level 1 = $255, Level 2 = 99.95, Level 3 = 314.93
Therefore collecting $15,000 would net $669.88

PLEASE HELP - NEED AS SOON AS POSSIBLE.
Thanks!