Oh, and on the original question: I've been using Xerox brand ink with the Canons, works well. However some of their cartridges seem to contain A LOT LESS ink than the original ones, making them much less of a bargain than they seem to be.
Top spot in ink cost currently is owned by my trusty old BJC-600 (the first ever desktop printer with single-ink tanks). Since this line of printers disappeared before the "cheap printers expensive ink" wave, its ink never got hiked up in price either. $8.99 buy me a double pack of any color ink tank - yes folks, that's a complete round of all four inks for $18.