How can I connect the sound from my laptop to my HDTV?

I have an older laptop with a VGA port that I can connect to my HDTV and display the video from it, but this connection does not include the sound. I am trying to figure out the best way to get the sound to also hook up to my TV. Essentially I need to connect the 3.5mm jack to the TV somehow. What type of (converted) cable will I need to do this? Where can I purchase the cable(s) from on the cheap?