We use different systems for road cycle touring and backcountry hiking. Road touring, we never take any paper maps. Instead we put TCX files on our Garmin Edge 800 and navigate with that. Works great. Paper maps are just nasty when road touring. We have no intention of ever stopping to try to figure out where we are or where we should go, especially in the rain. We just ride the bike. Road touring, we have no problem with recharging our Garmin and other equipment.

OTOH what you're doing is more like our backcountry hiking. We use paper maps for that because we're always stopping to look around anyway. We use USGS topo maps and draw our route on them in ink in advance. They come in a great variety of scales. https://store.usgs.gov/
And: https://www.adventurecycling.org/rou...in-bike-route/

We also take our Garmin Edge 800 with TCX files of our hiking route loaded into it, but we leave it turned off. We only turn it on if there's some question about where we should go or where we are, usually the same question. Thus the 12 hour battery life is good for many days. Your budget probably won't allow fancy goodies like an 800. We used just the paper maps for decades.