Is there a way to measure the amount of ink required to print a page? (Before Printing)
I suppose it is possible that you could write code that opened some utility that Access could use and then looked at every report before you printed it. You could count characters in every control (including labels), noting their font characteristics such as density, size in points, and other features like "Bold" or "Italic" and "Underscore" - but that isn't enough, since there is ALSO the matter of shading and backgrounds, such as white print on black background, or a "watermarked" page with a company logo. Then, you have the issue that one picture consumes as much ink as two or three pages of dense print or more equivalent pages than that with normal print density. There will also be differences in how much ink is used for .JPG vs. .WMF vs. other picture formats since printers do not treat such things uniformly. AND of course if someone brings you a file in a format that Access cannot open (because either the format doesn't expose its structure or it would but you don't have the right .DLL file), you would have no way to develop an ink-usage result.
Tracking such a thing would be incredibly hard and it would be trivially easy to miss something in trying to program this ink estimator tool. The more you try to pre-analyze this, the harder you make it for yourself. I'm noted for being fairly self-confident, sometimes to the point of being a bit arrogant in my ability to program difficult problems. This is one I wouldn't touch at any low level.
The point of me saying this is that I think you would do better to just develop page-level statistics that tell you "on the average, printing x pages in black-only will consume 1 cartridge. Printing y pages in color will consume 1 set of color cartridges." Start with the vendor's statistics on how many pages you can get as the basis for your rate charges. Then adjust your pricing accordingly according to pages printed by giving everyone a pro-rated share based on page count.
With per-page statistics, if you discover you have not been charging enough, just announce a price adjustment. It will be FAR easier to do this statistically. AND you can just figure in the paper cost, ink cost, and printer wear/maintenance/eventual replacement costs into the paper cost.