I've got a reasonably accurate method of estimating paper and ink costs, but what about the cost of the printer itself. How would you account for usage costs of the printer based on it's expected lifetime? Not sure how you'd rate printer life - square feet; lineal feet; or ?
I would say 4 years or any of the volume limitations set in the HP documents on warranty, service etc.
Counting the extra 3 year warranty price on top of the purchase price in that 4 years may be a wise thing, whether you have the extra warranty or not.
The heads are replaceable though. Warranty 1 liter ink per head, practice says 2.5 liter according a review.
met vriendelijke groeten, Ernst Dinkla