Price Break sum

I need help in writing a sum to calculate the following sum, hopefully this example will make sense. We charge a monthly fee for airtime to our distributors, we have three prices break 1 to 100, 101 to 500, and 500 to 1000. So i need to be able to calculate how much a distributor would be charged for there number of licenses at the end of the month. For example if they have 550 licenses at the end of the month it would need to be charged similar to this, the first 100 would be charged at £10, 101 to 500 would be charged at 7.50 and anything over 500 would be charged at £6. is it possible to write a sum for this. any help greatly appreciated.

If you have the number of licenses in A1 you can use this formula for the total charge

=SUMPRODUCT((A1>{0,100,500))+0,A1-{0,100,500},{10,-2.5,-1.5})

...or another way.....

=A1*6+MIN(A1,500)*(7.5-6)+MIN(A1,100)*(10-7.5)