If you're serious about avoiding cartel-level prices on ink cartridges, or even refilling services, you can convert a multi-color inkjet printer into a continuous inking model for serious long-term savings.
DIY bible MAKE's blog points to an oldie-but-goodie tutorial from 2002 by Eddie Matejowsky. His multi-page, in-depth tutorial explains how to convert the ink tanks in an Epson Stylus 760 to accept continuous ink refills, bought in bulk at serious discount, and how to piece together a custom circuit board that keeps the printer from demanding you hand over your credit card when the cartridges run "empty".
Matejowsky's project is not a one-hour lark, and it takes a few tools that semi-pro tinkerers may not have handy. It can, however, be worked on other printers, as Hack n' Mod shows a Canon printer with continuous inking. Commenters there also point out that you can meet your big savings halfway by buying an continuous inking kit for something close to $US50 on sites like eBay.
Tell us whether you'd ever attempt a total printer conversion like this to save money, or if you've found another way to beat the printer cabal at the ink game, in the comments.