Get the monoprice dongle if you need one. The workaround (breaking off that piece of plastic) , and some other retail dongles may give you some HDCP issues, such as the xbox rebooting if you change video sources on the TV.
MS released an adaper that contained RCA ports along with the TOSlink port, and it fit with the HDMI cable in place. I own one. I don't, however, remember how much it cost. Maybe ten bucks?
The official one was only available new with the purchase of an Elite (when it was actually bundled with an HDMI cable and the dongle) or with the purchase of the official HDMI cable that was bundled with the dongle, which was $50.
Used, the price could be anything, I bought mine for $4 from the thrift store I work at.
R.I.P. Eve English (Feb. 12, 1968 - Oct. 13, 2010) Momma Eve, you will be missed.