If you really want to save money then try refilling the cartridges yourself.
I've refilled cartridges for Lexmark, Canon and HP for over 11 years now and my current cartridges (for HP F4580) cost approx 33pence each to refill (and 30 minutes total time) whereas two new cartridges (300XL high capacity) would be approx £35.
Also, by using a small digital scale it is a simple matter to check on how full/empty the cartridges are and to inject the correct amount and avoid any over spills.
Cartridges should be refilled BEFORE running empty in order to avoid the print head drying out and causing partial blockages.
The following site is good for refilling information and refill kits can be bought in most cheap shops or supermarkets.
http://www.stratitec.com/