Printing Costs
There are five elements to printing costs:
The cost of the printer;
The cost of the ink;
The cost of the paper;
The electricity;
The space that the printer takes up.
Ink
Figures from the manufacturers usually assume 5% coverage of an A4 sheet.
This is equivalent to about half a page of text.
A full page with a couple of small pictures will cover about 15%.
See
Quality Logic / Kodak: Cost of Ink per Page - UK.
Mutoh America Knowledgebase.
Printing Companies usually use the CMYK (Cyan Magenta Yellow Key (=black)) method,
where each of these four inks is applied in turn.
See e.g. Print Express
Cheap Print House
Paper Size
See Paper Sizes.