Well each printer uses a different amount of ink per usage. With my Lexmark and Epson i could get about 30 full color pics done before i had to buy more ink. If it was even that much. As far as Documents you should get roughly 50 or more of them printed.
I would seriously look into a Kodak Printer. That way if the ink goes you can get it cheap rather than spent $50 on a printer and then $50 everytime you want ink.
I am currently looking into a Kodak myself. I know someone who works there and has 2 of them already and they are great printers. For both pics and docs.