Kodak ink carts are cheap, but they are also low capacity so need replacing a lot more often than other ink carts.
I installed an HP printer in an office a year or so back and beforehand checked the ink costs. The carts were more expensive than the Kodak's, but the HP carts had more ink in them and so worked out a lot cheaper, especially when using the XL carts.
Kodak standard vs XL cart yield - 205 vs 430
HP standard vs XL cart yield - 420 vs 1200
Kodak 30series black inks prices - £7.99 std/£12.99 XL
HP 920 series black ink prices - £11.07 std/£18.50 XL
So Kodak is about 4p per page std cart and 3p per page with an XL cart. HP is about 2.5p per page std and 1.5p per page with an XL cart. Both for a mixed graphics/text print.
This is based on the companies stated cartidge yield but real life usage often shows these figures to be optimistic
Mark.