That's a great price for the SteriPen, which normally retails at $150. Note that there is a newer model recently out and Piragis seems to be selling the original model, at least from looking at the picture on their website. REI's online catalog says that:

"...Newest SteriPEN features easier battery access, water bottle and military canteen compatibility and a new slimmer carrying case..."

These are handy improvements, but if that's it, then functionally, the original model should be just as effective at purifying as the newer model, at 30% less cost! <img src="/images/graemlins/smile.gif" alt="" />