I picked up 3 cartridges for my 480, two black and one color. The black has lasted longer then the cartridge it shipped with (although I have this feeling they shipped it half full or something). I paid less then $15 shipped for all three. I haven't needed the color cartridge yet.
Edit: Some manufactures say it voids the warranty on the printer, but the way I see it, I paid $20 for this printer after rebates. I'll just replace it if using aftermarket ink breaks it. I'd have more then $20 in a color replacement cartridge from epson.