Wiring Harness

I am trying to prepare myself for this summers addition of The Poor Boy's Stang Restoration Cronicles and I thought I'd pick you guys brains for information on replacing a wiring harness.

I'm sure many of you have experanced the excitement of having random headlight outages during a late night drive. Scarry!! I fixed that problem with a few relays, wire and a switch. While it works well I'd like to incorporate it into a new wiring harness. I've got a 73 mustang and have been in need of a new harness for years. I guess the old wires have lost there ability to carry much of the current without producing alot of heat and many of my accesories are not working properly.

Anyway I wanted to ask you guys if you had any experience with replacing a wiring harness. I have seen the harnesses that painless makes and one of those would work but gee does it really have to cost that much? I am thinking I could get a used fuse box from the local junkyard and combine that with new wire from somewhere (what I've seen at the hardware store is pretty limited) and make a new one for less than 80 bucks.

Well let me know what you guys think.
Thanks in advance.