I have a 55lb thrust Minkota trolling motor that pushes my drift boat maybe 4 or 5 miles on a 12 volt battery. I have a solar panel too that helps keep it running on a long day.
That same motor might push a styrofoam/fiberglass surfboard or SUP board boat all day long.
Too bad I'm 2000 miles from my shop. I may have to move my shop down here, so up North is fishing only.
Or have a shop in both places. There are small one man trolling motor boats out there already. I haven't seen a totally minimalist DIY one built like a wide surfboard yet. If you already had the trolling motor the boat board would cost maybe 200 bucks or so.