I spent some time trying to fix what seemed to be a similar problem on an HP and in the end it turned out to be that some of the flexible connectors to the print cartridge cradle (the ones that carry the current to that the ink and blast the tiny droplets out, one for each part of the spray pattern) had fatigued and failed - and were not available as spare parts.

The really cheap printers, particularly Lexmark, have ludicrously expensive ink. Multicolour multifunction lasers are just starting to become affordable. I think there is a Minolta at about GBP 300. A barrister friend bought one a few months ago and was very impressed. The running costs are a fair bit lower than the few inkjets that have reasonably priced ink (Brother are about the best in that respect, but they have discontinued the MFC590/890 range which used huge ink tanks and so were cheap to run).

An economical laser will print a black and white page at about 5% coverage for about 0.1 p whereas an economical inkjet is about 1p at best and an expensive one about 5p per page. So you could get your money back in about 6,000 pages, that's under 3 big boxes of paper if your inkjet would have been a Lexmark, and about 15 boxes of paper if your inkjet was a Brother MFC 890.

Good printer sellers will know and disclose the running costs of thier printers.