I wish to look at this in terms of CO2 footprint, rather than ink consumption.
Some random source on the internet suggests that the CO2 footprint of a toner cartridge is around 5Kg for a new cartridge or 2Kg for a refilled one.
The laser printer in my office gets around 31,000 pages at 6% coverage, or around 2,000 pages 100% coverage. Arguably with 30% coverage of full page text you can get 6,000 pages per cartridge.
With these figures we can estimate that the CO2 footprint for the ink consumption is between 0.16g to 0.83g per page.
The CO2 footprint to manufacture one piece of A4 printer paper is 4.17g. So the ink represents between 3% to 17% of the CO2 footprint from printing.
You might be able to optimise ink consumption, and find the most readable font that uses the least ink but its only going to have a negligible effect on the environmental impact of printing.
If you really need to read something, then keep it on a screen, reduce ink consumption by not printing.
If you really do need to print something, like if your life depends on it, than choose a font that looks nice and will have the most impact to the person who is holding the sheet of paper, rather than agonising over a small fraction of resource consumption.