Everybody probably remembers exponential equations from high school e.g.: y=x to the power of 2. You would get a nice parabola trying to become a vertical line but never really getting there. That would be true for all exponents bigger than 1. Only an exponent of 1 would give a straight line.
However, an exponent smaller than 1 gives a parabola shifted through 90 degrees, trying to become a horizontal line but never really getting there.
And this is ideal to reflect discounts of a technical origin.
We used the principle for discounts for bigger models: Once you've got your printer running, every next cubic centimeter will be slightly cheaper than the one before, since you're spending your fixed costs thinner.
To demonstrate I've set up an ABS material with a very simple calculation parameter: price per cubic centimeter, 1$.
However, I put in a "special price" "power for volume" (an absolute misnomer, that's what you get when you don't involve your UX specialist) of 0,9. To make everything even clearer I put my VAT to 0%.
Then I uploaded 10 models, from 1 to 10 cubic centimeters.
the first one is OK: 1 to the power of 0,9 is 1.
I'm not going to show all the uploads, just the lower part of the cart:
This is what Excel gave me as the solution:
Seems to work. The difference of one cent is due to the inherently inexact nature of .stl files.
Please try yourself, using a spreadsheet like Excel to find the correct exponent for your case.