Hello!!! Here is what im trying to do!

I am trying to set up a commission scale for promoters that pays them $2 per
unit sold if they sell under 100 units.

If they sell 101 - 200 units id like to pay them $2.25 per unit.
201 - 300 units they get $2.5 per unit

How can I do this in a sensible way that organizes the commissions and shows
me the sales person's total commissions.