Very true if just one or two of you it would not make sense. But i do know those who are real heavy users ie young families etc have worked out how much they will save and then used for a good few years and its worked for them. Amazing how many pages a family can end up printing now for school work and it appears it can vary from so many copies free to paying quite a bit if you print at the school college!
Whatever printer you get make sure it does not use cmy for black as some cheap printers do!! Most print is black and I have seen some printers where they combine the cyan, magenta and yellow to make the black and they will waste ink like crazy. Especially on text which is typically black.
Same with making sure you can buy/change the indivudal colours seperately Also check how much the black ink/toner is often they are far cheaper than the colours
Amazing how many pages you can print in black and white mode or even in another mono colour if you have an excess of one colour ie drafts, written notes, web bought items recepits and some other printouts which are throwaway after a limited life.
Picking the right ink jet is very important as some waste ink like no ones business so worth checking the interweb and the manual about how often they do clean head etc and if it can be altered and how it will effect the quality