The cheapest one I know of is DVD2oneX. There was a freeware one on sourceforge.net, but it hasn't been updated for well over a year, if memory serves me. You can do what you want with ffmpegX, although it's not entirely straightforward, and I personally have not used it that way, so I can't tell you how well it works. I've only used ffmpegX for mpeg4 compression.