I have a Garmin GPS III that I bought in a pawn shop for $50 when they were going for $350. It has served me well.
I used to use it for search and rescue. Those of us with GPSs would track our searches, then download them into the IC laptop to log what areas had been searched.
I have tracked mine with a laptop and it is a great way to go but you really need to have it mounted securely and convieniently, which can be dificult.
I can't load maps into mine, only from it to the PC.
If I were shopping for one now, I would look for a GPS III+ or GPS V (both Garmins) that I could load maps into. A used one could probably be found for cheap.
And they make great speedometers when your tire size is off.