If you mean refilling the old cartridges, stay away from it. I have found it to be more of a bother than it is worth, it's messy, and more importantly the ink is very watery causing bluring and smearing. If you mean off-brand ink cartridges I would also proceed with caution. First of all, you will want to double check the amount of ink per cartridge, that may account for some of the savings. Generally OEM ink will give you perceptibly better quality as it is developed with at least a tiny bit of concern for a specific printer type, Epson especially as they use a different ink delivery method than other ink-jet companies. If you're not going to be printing presentations of extremely important documents replacement ink will likely be fine, but OEM will generally give you a higher quality.
Aaron Meyer