Thanks to the internet, I have been able to research different audio set-ups. Check out - http://youtu.be/CiRWiVq5otk
I have selected a digital audio recorder from Sony. The Sony icd ux512 retails at $99.99 but is available from Amazon for $75.
The cabling set-up is so simple and discrete. I can plug in my headset to a patch lead from Barnstormer Audio. It comes with three connections. One end connects to my David Clark headset. The other end connects to the regular audio socket in a C172. I then connect spliced end of the patch lead directly into my audio recorder. It's that simple!
Next I need to focus on the video. I have an idea to use a small HD camera, but I am first going to get the audio nailed. There is no point having video with no audio. Also, I don't want the audio and video to distract from the task at hand. Let's take our time.
All going well, I will be recording my first cockpit audio in about two weeks time. In the mean time, I will continue to watch and admire Rick's YouTube channel.