I saw this ad from Alibaba for HP 685 CMY and Black ink cartridges,
These can be used in HP 3525 , 5525, 6525 ,4625 ,4515 Ink advantage Printers
http://do-it.en.alibaba.com/product/815085221-218232230/hot_refill_cartridge_for_hp_685_670_655.html
He said it would cost 16$ per set with 36$...