As MT mentioned, I used a Steripen Adventurer for the first time this summer.  It cost me $60 as I recall.  It uses two CR123 Li batteries that cost about $2 each.  I was able to sterilize about fifty 32oz nalgenes before changing out the batteries.  Took about 75 seconds each time.  The only problem I encountered was sometimes the device turned off during the purification because I'd get the sensor too close to the top or inadvertently let it out of the water.  Once I got used to swirling it around, no problems.  To dry after using, I'd wipe off any water on my sleeve or pant leg before storing.  Was concerned about storing it wet, so a couple times I'd leave it out to dry out real well.  For a solo trip, it worked wonderfully.  Wouldn't want to rely on it as the only purification means for a group trip though.