wow ... I thought I'd see a lot of web based rip-offs in my day, but Ripoff-City charging $3.99 for a single voltage regulator, wtf!
here's the same part from Future (they're Canadian), $0.15:
**broken link removed**
I'd recommend you find a Cig lighter to 5v usb charger on the intertubes somewhere, and modify it to accept a 9v battery and a switch. Most of your 12v to 5v usb chargers use high efficiency switching regulators to drop the 12v down to 5v, so they operate a lot cooler. The same regulator will also accept 9v from your battery and drop it down to 5v as well.