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GIS guy here.
Check out Bad Elf GPS units. If literally all you need is a GPS signal, these will do that for pretty cheap. You can also tether it to your phone with bluetooth and replace your phone's internal GPS signal with that of the device. They also make GNSS connective units, but they're much more expensive.
Theres no single best option for GPS units-- do your own research.
As for navigation, I usually recommend Avenza maps. Loads a georeferenced PDF and displays your location on it. I assume you're in the US-- the USGS publishes geoPDFs of the entire country for free online. Go wild.
