I buy my cartrtidges for my Epson CX8400 from eBay, usually from a supplier in BC. They work well, and are a fraction of the cost of paying regular retail for Epson branded cartridges. I have been doing this for years, with a previous Epson printer as well, and I cannot recommend it enough. It has saved me bucketloads of money over the years, and allowed me to print in full colour for my business needs without worrying about the high cost of doing so.
My last purchase was for 29 cartridges. Total price, including shipping was $47.80 CAD. I won't even try to calculate the cost of buying these Epson branded from BestBuy or Staples! It would probably make you puke! lol