Here's an example of some prints from yesterday:
5x prints, 100% coverage (zero white to be seen after printing, Shutterstock images), 23 sq.ft (2.16sq.m) each.
Average ink per print - 32mL
Average ink per sq.ft - 1.4mL
Cost per genuine ink tank (700mL) - USD$123 (AUD$165)
Ink cost per sq.ft - USD$0.24 (AUD$0.32)
Please note this is pretty much worst case scenario, as the images printed were quite dark.
Another 6 panel job today, ink usage was 2/3 of the figures above as they were less intense designs.