Some thoughts.

1) You want a terrestrial not aviation map as your crew is driving to
find you, not flying.

2) What I have is the most inexpensive GPS I could find. I think it
was a Gecko from Target. All it can do is point you the way to a
LAT/LONG and leave a breadcrumb trail.

However it is not particularly simple to input LAT/LONG and a base map
would be useful. Therefore I might lean towards a used unit with
better features.

3) I believe that Garmin has the best devices.