My 2nd 300 broke over he summer like yours did. Fortunately I bought a Warrantech extended warranty, and they sent me a check for my original purchase price. I'd highly recommend Warrantech. As of now, I'm using a headset with my 300 and waiting for the 650 to appear!
Also, you can get a replacement shell for the Treo 300 here:
http://store.craytonelectronics.com/tr300resh.html