As the others have said, manufacturers sell ridiculously cheap printers and then make lots of money from selling the ink/toner.
I never buy branded cartridges. I have an Epson Stylus injet printer. The last time I bought cartridges I got 2 sets (5 cartridges in each set) for £10 - a MASSIVE saving. There may, as one person suggests, be some printers that won't work with non-branted cartridges but I've never had one. I've used them on Epson, HP, Oki, Canon and Xerox without problems. I only buy from companies who guarantee that their products will work.
A laser printer is much cheaper to run than an inket and, for most purposes, produce better results.