How to use sensor to measure amount of ink used for each print job?
I think you are on a thinking track that is a non starter. Trying to make something like this is so printer product dependent that you will never be done. Printer manufactures are coming out with new printer models all the time and new technologies are constantly being added.

If your idea really does have merit, I have my doubts, you would probably be best off seeing if you could partner with a printer manufacturer to productize your ideas in their next line of printer models. Marketing could be leveraged to capitalize on the feature's value.