I just picked up an HP iPaq 4155 off eBay for $199 plus shipping, and it does much more than my Treo 650, but no phone, including 802.11b wireless and Bluetooth. It's the same size as my old Palm Vx. There's a new model iPaq (9150 I think) that is same size, but omits Bluetooth.
All that said, I'm having a real tough time convincing myself to go back to two devices - once you converge, you lose the urge (for two).
