sometime ago I found a site called Inkgard that sells their own HP cartridges that have much more ink in them for a cheaper price and include a free software DVD to allow you to decide what ink-usage level to use for each print job. For instance to save 10% up to 90% ink. Can't find my receipt, but a really good value and you don't have to buy them so often.
http://www.inkgard.com