After a somewhat similar experiance I managed to talk around a chap in accounts. After seeing all of the figures he agreed that it would be cheaper to buy a large stock of second hand network printers off of eBay that use cheap replacable parts and sodding huge yet cheap cartridges. These printers do one thing (network printing) which they do quite well.
Print costs fell from £3k per month to £3k for the entire of last year, including maintenance kits to keep the fleet working in good order.
Last time a print management company came into my place they were a bit shocked to discover that my real world costs including parts and paper was below the "on paper" costs they were quoting.