Price estimate-far more than the entire bike is worth. Hopefully you can do the work yourself. As for the wiring harness being a bear, It is no worse than any other. You do not mention if this is a 750 or a 400/450 model. You can get a decent one from a salvage yard up in Bear Delaware that had a few of the 400/450 sitting out back. Don't know about the 750 harness.
As for any wiring harness-start with removing the tank, seat, and side panels, then remove the headlight and disconnect after labeling everything in the headlight bucket. Start working your way back. Feed the harness up around the steering stem and into the headlight, making all connections around the headlight, turnsignals, handlebars, then working back do your coil connection and do the connection to the main power panel under the right side, I believe it was, then weave the harness around the main frame and down the frame to make the connection for the rear fender and turnsignals.
Curious, why did some of the wires burn or melt? Better to correct that problem while you have the bike apart.