Wiring kits?
The money is in the different colors of wires and the schematic you get with the kit. It takes time and a meticulous mindset to map out their own electrical diagram for the entire vehicle. If you don't already have a stockpile of wires in different colors and gauges, it would cost quite a bit purchase these. I couldn't imagine troubleshooting an electrical problem with all the wires the same color and gauge from a single spool of wire. To those with the time, skill, and just love for that sort of thing; I recommend going out and finding a newer vehicle at a junk yard and cut out the longest bundles of wire you can so you can have your colors and gauges. However, I do get your point on the insane prices of some of these wiring kits. I've heard of sets costing upwards of $1k because they made just for your model/year vehicle. Aside from maybe the one at the very top of that list, they don't even take the time to measure wire...that's too much time and work. All those kits are really "universal" when they are advertised as otherwise. Me, I purchased a RF kit for about 300 on sale. To me it was worth it because I had a set amount of time to finish the project and by having all the tedious work of diagrams etc. already done for me. But there's no way I'd pay upwards of 1k for a wiring harness lol