Keep your eye on the "Coolbox Blizzard" deals, as these pens have been up a bunch of times at a significant discount off of sticker price. (I think I got two for $10 or something like that.) You'll still get the DVD, as at that price, it wouldn't likely be worth Penguin's while to sell just the pens and discount it further.
If like the effect so much that you've worn it out, you may want to save your pennies and consider Chris Smith's "Ignition," which is essentially the same trick but with a car key. It costs more, but is much better made than the pen, seems more natural, and is much easier to carry around, as you just attach it to your key chain.
Ignition has also been featured as a Cool Box special and will likley come around again if it's still in good supply.