Thanks for the responses:

Its never until the first responses that you realize how vague your question was...

Sale 1 is worth $75, 2 is worth $100, 3 is worth $150, 4 and beyond is worth $250

So, 2 sales would be $175 ($75 + $100)

3 sales $225 ($75 + $100 + $150)

4 sales $475 ($75 + $100 + $150 + $250)

5 sales $725 ($75 + $100 + $150 + $250 + $250)

Etc....

Does that clarify?