Botach via eBay offers the Uzi Tactical Glassbreaker Pen 7 in Black or Gunmetal for $19.99 with free shipping. That's the lowest price we could find by $9. It features a pocket clip and has a glassbreaker on the tip.
I'm a big fan of the Uzi tactical pens - they're aircraft grade aluminum, meaning they're really lightweight but still very strong. Just a note on the glassbreaker aspect, to be used for life-saving purposes only: You'll want to hit one of the lower corners of the glass, as that's most vulnerable- not the middle. And an even easier method is to jam the tip of the pen between the rubber and glass and pull down to crack it.