If I understand your setup correctly, you would only need one HDMI cable from the cable box to the TV. Unless of course you have a BlueRay/HD DVD player, in which case you would need two.
A friend of mine decided to buy a $4 HDMI cable from Ebay. It lasted a little over a week, only because he would switch back and forth between his PS3 and cable box. I would recommend shelling out the extra cash for a good cable. If you have any friends that work in retail electronics give them a call. In my experience these cables are marked up quite a bit, and with the right discount can be had for under $10.