I bought the 2006 version used on diaperswappers.com. I too wasn't sure if I was committed to it or not and DH was majorly skeptical. Well, when I had the birth of my dreams, I would have happily paid full price. Also, as our hospital bills arrived and were thousands of dollars less than my first birth with an epidural and all the extra costs that come along with it (anesthesiologist, iv, pitocin, etc. - we have sucky health insurance that left us paying nearly $10,000) I realized it was most definitely the best investment of $50 I've ever made.
Definitely look around for a used version if you want. The hypnosis for childbirth forum at BabyCenter is also a great place for more info and to find people selling their Hypnobabies material.