You don’t have to go nuts with spending… but I know that car GPS’s don’t really work, since you are 99% off the road for Geocaching.
You can use the Groundspeak Geocaching app for the iPhone, but we cache in such bad weather/spots that I’d hate to have to carry the phone out in the open for hours and risk it… and I don’t know that the iPhone GPS is as fast/exact as a dedicated GPS for getting within a few fee of something… it could be a cheap start though, if you have the iPhone anyway. Oh, and it’s a great app for going paperless and has tons of great features. Well worth the money. And there’s a Free Version to play around with first.
We have a Garmin eTrex Venture HC… I dunno, around $125? And it’s perfect. You do want one that’ll hook USB to your computer, so you don’t have to manually enter the coordinates.
DON’T get a Magellan. The one I bought had issues, and they refused to repair or replace it… said it was discontinued, even though I just bought it. Go to Geocaching.com and see what people are saying they like.
There’s even a very simple/inexpensive one that comes pre loaded with caches… mostly to get kids started. But I like the multi-use of a full GPS.