I stick with OEM ink, personally, but I'm a Canon owner and the inks aren't quite so costly per volume, I don't think. But I also try to be pretty frugal about what I print out.
If you go the refill route, just be aware that you risk getting a permanent head clog. Some people refill for years with no problems, but I've heard a number of stories of people who had to replace their print head (or the printer itself) after refill ink clogged up their print head. Sticking with refill inks that you see other people have success with would be a good start.
I also second the recommendation to get a cheap laser if you're doing lots of B&W document printing. You'll get better text quality at a much cheaper price per page.