where is the best place to buy ink cartridges at a discount price?

I use a lot of ink, for home and my business, I have a HP printer that also scans and copies. Becasue I use it in my real estate business I go throught a lot of the ink, there is two cartridges one is tri color 28 and the other is black 56. On my HP I seem to always have a line or two that does not totaly come out in print, its prints – only the top have of the word prints almost like cutting the bottom have of a line right out please help in both problems, I have done all the clean, aline etc. But if I change the ink, it works, but sometimes the ink is only half gone when this starts to happen and I need to change the ink? the ink site to buy the cartridges far less themn 30 dollars a pop. Help Help?

printpal.com ; inkpal.com Go to Google and type ink. Printpal is good. $5 for a $25 OEM cartridge.