What Gps Unit Is Good For Desert Trail Riding?

I am looking into getting a Garmin Etrex. I don’t know whether to get the Vista or a more expensive model. Keep in mind, this GPS will be used to keep from getting lost, and to mark spots I would like to remember. I have heard that downloading maps costs almost as much as the GPS itself, so I am a little wary. BTW not looking to spend more than $250. I don’t really care if the screen is color or not.
I do a lot of ATV riding in the desert mountains of Arizona. Lots of the trails look very much the same, and it can be very easy to get lost.