Start from the yield baseline. Cartridge yields are commonly rated on standard test pages at around 5 percent coverage per colour, under ISO/IEC 19752 for monochrome toner and ISO/IEC 19798 for colour. Your supplies cost per page at that coverage is the cartridge price divided by its rated yield. That is the baseline you already know.
Read the job's coverage. Open the PDF in InkQuote. Each page gets a C %, M %, Y % and K % estimate, and the All row gives the document figure for each colour, weighted by page area. A page at 20 percent black asks for roughly four times the black toner of the 5 percent test page.
Scale the baseline. Divide each colour's job coverage by 5 to get a multiplier, apply it to that colour's supplies cost per page, and add the colours together. For a job averaging 15 percent cyan, 12 percent magenta, 10 percent yellow and 18 percent black, the multipliers are 3, 2.4, 2 and 3.6. Yields in daily use move with the machine and its settings, so treat the result as a working estimate and tune it with your own records.
Count the pages in a copy. The Quote page treats one copy as one printed set of all pages, so the price per copy you type should cover every page in the file. The document figures already include every page, weighted by size.
Watch the black channel. Text set in solid black, whether the file stores it as CMYK, grayscale or RGB, is measured as black toner only, so text-heavy jobs keep their colour figures low. Grayscale images and fills count as black as well.
Keep the figures with the job. Export quote sheet saves one page with the page table, the document total, any spot colours, the notes and the quote, as a new PDF. File it with the job ticket so the next reprint starts from the same numbers.
Keep the artwork private. InkQuote runs on your Windows PC with no network access, and the customer's PDF is opened read-only, so nothing about the job leaves the shop.