The cost per print of the OfficeJet 5255 is mediocre. The cartridges cost nearly half the price of the printer. Not only is the price-per-page quite high, but the more you print, the more you end up spending in total.
Keep in mind that even if you print only in black, most inkjet printers continue using the color cartridge for servicing tasks, so you will likely still need to replace it eventually.