You could always have two kits: One with the parts and wires, and one assembled. That would eliminate some of the time necessary for building all the harnesses.
For a pre-built kit, I would pay $80-100. For the built-it-yourself kit, I would charge parts + a reasonable markup for your sourcing the parts, maybe $30-50?
2012 Mitsubishi i-MiEV ES (lease ended) • 2015 Nissan LEAF S • Tesla Model 3 reserved
Mods: Matte black Juke wheels, LED headlights and accessory lights, horn, CarPlay receiver, subwoofer and amp