I would still recommend to get a large phone/tablet, and install osmand+ or organic maps, and download all the maps for places you travel usually (maybe your country or state). In osmand, you can also install more data (like roads and highways, topography or eleveations, or the wikipedia entries, so you can also look up photos) they work great with gps, and very flexible, can also be used for entertainment. I would recommend just get an old tablet, if you know how to install a custom rom, if not, then just set it once, and then don’t add any wifi or mobile network options.

The reason is, most offline gps are poprietary, and not that easy to repair in case broken, and are just as expensive (they charge for the sturdier builds, which is plus, but are moch more closed walled gardens)