I started with a Magellan MAP330. They are pretty cheap on eBay. You could probably find one well in your price range. The firmware will probably need to be upgraded to enable and correct WAAS functionality. To go paperless, I purchased a $10 software package for my Motorola Q phone.
It is a hassle to use three devices (vehicle GPS, Q for field notes/logs/hints, and the Magellan for navigation to the cache) but it was good enough to help me decide if I wanted to invest further into the hobby.
My new PN-40 arrives in two days.