You could always get a handheld GPS.
If you are into other outdoor things like hunting etc.
If you do not have other uses, then I bet it would be as cheap to just buy the GPS build into the unit.
Garmin makes a few models that float.
I use an 778C and have it wired into an handheld Garmin.

It is nice to past something, notice it on the screen and mark a waypoint