We have a dedicated Xerox Phaser 6125N. (a Laser Printer) We only use it for color documents, and have several HP 4100s around the office for b/w printing. We get our Phaser cartridges from ink4less.com for $10-15 each. I'm not sure of exactly how many pages we average each month on the Phaser. Maybe around 3,000 for the last few months, maybe much more. I don't think we would get a new one until our current Phaser breaks down, unless we find a significantly cheaper alternative.
The Phaser is out for repair (was squeaking pretty badly) and the repair guy is suggesting we buy a solid ink printer to replace it. Does anyone know about those? I'm concerned that 1.) the ink can be scratched off with your fingernail (according to wiki), and 2.) the heat in Texas would melt the ink during delivery, especially during the summer when the docs are being driven around in the back of a truck. The ink sticks are also significantly more expensive; I haven't found a 3rd party provider. I'm not sure if the higher output pages per block would be worth it.
Thanks for your insight!