Just take into consideration that it might not be “marked up” but instead you’re paying for additional circuits that provide safety features. Then consider those features non negotiable. You could build a motorized 4 wheeled vehicle cheaper than a car by just making it an engine with wheels. You could save on brakes, airbags, crumple zones, seatbelts, and all sorts of other things. But you shouldn’t. Just use solar panels, a properly sized inverter, a charge controller, and deep cycle marine batteries.