black ink only printers?

[#1]

I just got an IP4500 of freecycle, to replace my IP4200. Luckily they use the same ink 
But yes you get ~2000-3000 pages from each toner cartridge on a mono laser, and they can usually be refilled. I freecycled a HP LJ6 a few years ago, still have my monster of an LJIII and an LJ4 that haven't been powered for many years. Parallel only, I do have a usb->parallel cable somewhere but don't know where.

[#2]

My HP 3050A definitely works with only the black ink cartridge installed - it's a few years old though so might not be available now. However the HP 2540 (2542 from Argos) also works with only the black. Price is around the £40 mark I think.