For those who want a cheap solution for a kindle-compatible USB solar charger, you can buy USB solar chargers from Chinese (or Hong Kong) ebay stores for about $3USD (including shipping). This one is rated at 5.1v 0.4w (about the same as charging from a host PC), but for a little more money, you can get one with more charging (or operating) current:
http://www.ebay.com/itm/USB-Solar-Ba...item27c87453f8
And with a USB cord, it lets the kindle sit in the shade while the charger is in full sunlight, so no need to bake your kindle while charging it. And while not charging your kindle, it can be charging your cellphone or camera or other USB chargeable devices.
P.S. I love the DIY method. But sometimes I want a cheap and simple solution too.