There are some tools to directly rip DVD to MP3 but just a cursory look and they all want some $20-$39. It would do an entire DVD in probably 20 minutes.
For the free route, you can use DVDx
http://www.wikihow.com/Rip-a-DVD-to-an-AVI-or-MPG-File-Using-DVDx
to make a Divx or AVI file.
Then use Media Converter SA to convert that divx/avi to an MP3.
http://www.mediaconverter.org/index.php?s=c&show=downloads
That’s gonna take a while depending on how long your DVD is.
You can also load the video into higher end video software like Adobe Premiere and extract the audio that way.
Check out Handbrake that I linked to. Some other FReeper (thankyouthankyouthankyou) suggested it a while back, and it has been my hands-down favorite since then. For Mac and PC.