It's worse than it sounds... You're not actually paying for ink, you're paying for pages, in a similar context to how you used to pay for minutes for your cell phone.
A buck a month gets you 10 pages printed, 100 pages printed a month sets you back $6/mo, and so on.
The ink is shipped "free" when your cartridge runs out, and naturally, they figured out how to increase the ink capacity in the carts to be much higher than the ones they sell, so shipping a cart out will be much less frequent if you're ponying up for each page you print.
Odds are it'll be cheaper over the life of your printer as long as you're a member of the residual income brigade...