Myself, currently, am poised with the situation of buying a new black ink cartridge for my multi-function printer.
The new black ink cartridge for it is, by itself, costing well over 60$ Canadian.
Now, I think it would be best, to replace the unit of about three years of age, by a much newer one that comes with its included cartridges. The color ones and the black ones can easily surpass a 100$ price tag. And, the new one, will come with the price tag of about 50 to 70$ + all taxes.
My suggestion to you, is quite simple, check how old is your current printing unit and, decide if the replacement of such unit would be more of sound investment than, to just replace its ink cartridges. Chances are: replacing the unit will sound a lot better, money wise. Second, if you can, try to use your color cartridges as much as you can. I really do not know why, a regular, home based, person should ever use the grayscale or drafting mode of such printing unit. Unless, you are an avid word processing software user and, not using any color pictures into such documents.
Conclusion: For home use, all-in-one printing unit and, for intense office use, a laser printer that can do drafting documents an almost costless use of it over several months at a time. As for me, a color inkjet should be good enough to use for my bills printing over the internet and bank statements + the occasional one single sheet word processing documents that I might need once a season or a year at a time.
Hope I got as helpful as I can get. 