I have an ancient, yet trustworthy HP6L black-and-white laser printer that I bought back in 19??
About a year ago, I replaced the last of a long line of crappy ink-jet color printers with an HP-CP1815ni color laser printer.
I assumed that for printing in black-and-white, the 6L, being black-and-white only, would be cheaper. I just looked up the prices of the toner cartridges, and their yields.
Turns out that the color laser has a lower per-page cost for black-and-white than the b&w. A toner cartridge for the 6L is around $75, and is rated for 2,500 pages, while the color printer’s black cartridge is about $90, but yields 5,000 pages.
Lesson for the day - check your assumptions!