Anybody who sells Monster cables is going to charge at least $90 for a 3-foot HDMI to HDMI cable and at least $100 for a 6 foot cable.
Try RAM electronics
http://www.ramelectronics.net/html/DVI-hdmi_cables.html
Avoid buying extremely cheap HDMI cables ($10-$20 range). I bought a 6-foot $14.99 HDMI to HDMI cable from TigerDirect.com. It had a broken or loose wire inside the cable near the end of one connector. You had to hold the cable just right to get a picture and sound. This cable was made by Cables Unlimited. TigerDirect.com also had some 6-foot cables that were around $25. They were made by BAFO, but I am now leery of all cheap HDMI cables.
Amazon.com sells all kinds of different price range HDMI cables.
Check with your local cable company if you can get HD cable from them. They may have a DVR or HD cable box with an HDMI output. My local cable company (Bright House) sells a 10-foot HDMI cable for $49.95.
I think if you stay in the $40 to $60 price range online, you should be OK.
Do a Google search for "HDMI cable". You should see lots of choices. Just avoid the extremely cheap cables.