entering discounts AND DISCOUNTED TOTALS on invoices

I have some invoicing that I need to reflect a price of say $17.00 per
unit. Then I need it to multiply by lets say 56 units and total. So far
easy. But I want it to then say something like "pay by July 1st and
get a $1.00 discount per unit" - and then do the calculation and give
the new total.

So I would like BOTH TOTALS to appear - one for payment after July 1st
and one for payment before (discounted TOTAL price for early payment).
I do not want a "pay after such and such date and add a $1.00 or
percentage", rather I want a discounted price for early payment and
totals for both? Any way to do this?