I have bought 2 Ipaq 3835 for less then $150 on Ebay.
They both work excellent, and the one I use has ALL my GPS stuff on it.
I use it to track myself via streets & Trips, and have a number of other programs for Geocaching.
The Ipaq is also one of the most expandable PDA's, it has literally hundreds of different accessories, main ones being sleeves for different cards, cables to interface with other devices, etc, etc ad nauseum.
You can add memory, wireless, GPS's, even a PCMCIA hard drive, there's even a digital camera attachment that turns into a pretty decent digital camera.