> Do colour toner cartridges cost much more than mono ones?
The 2550N has separate cartridges for each color, so you only have to replace what you need. They're about $90 each and are good for 4,000 pages. To give you an idea how long they last - the "low toner" alert came on last August, so I bought toner for when it was empty. I still haven't swapped them out.