Welcome. Honestly, there is no way to do a quality custom wiring harness cheaply.
Doing a cheap harness on the cheap, is more like spending time to replace the old problem with a new one.
If your good with electronics, and have the tools and skills, then no problem.
The biggest issue is how much time it takes to re-wire the car. Getting all the wire correctly routed in the harnesses and the right wire lengths, then crimping on all the connectors is time consuming. Not to mention the various odd-ball connectors (mostly the molded bullet connectors.)
If your just replicating the stock harness, then you can use the original as a reference, but if everything is custom, then it gets more complicated.
Anyhow, if your just restoring the car and NOT looking to add a bunch of custom electronics, the M&H Reproduction wiring harnesses will save you time and trouble, but look expensive at first glance.
Just as an example, I just did a custom wiring harness for Mocajavas '69 Coronet which has nothing stock at all. Custom dash, Speed hut gauges, TCI6x transmission, Full Sniper EFI, electric cooling fans, Digi-lights tail lights, custom shifter and console, re-located battery, ect.
He started with a nice Ron francsis kit and the additions to the kit. Not sure how much he spent on just those parts, but likely close to $1,000?
We spent many weekends wiring the car with several stoppages where we had to order needed parts, supplies, tools, and additional wire that was not part of the kit(s). I was doing this as a friend, but Mike being the nice guy he is gave me some money, which I spent on more terminal crimping tools.
I had the MSD pro-crimp tool, and most of the dies to start with (about $250-300 investment), but got tired of having to swap dies, so got another MSD crimp tool ($96.) These were used mostly for the Packard 56 terminals and the spade lug terminals that connect to the Ron Francsis fuse block.
Then there were the Packard 59 terminals for the headlights. The kit came with pigtails, but I really didn't want to mess with splicing in pigtails when it's easier to just crimp on the terminal, but it takes a different crimper, so another $100+, Not to mention the battery cable cutters and large lug crimpers.
So, now we have a pretty big investment in tools and time, and the harness still needs to be wrapped. The Ron francsis kit did come with some braided wire covering, and smaller heat shrink for splices. In addition, we got a few more different sizes of the braided wire covering, and large heat shrink to terminate the covering ends, plus a few rolls of electrical tape, and then for under the dash, the split type covering with velcro. The TCI trans connector is close to the exhaust, so those wires got a high heat wire covering, along with the starter wiring.
Also, be careful of the quality of the terminals you buy. The metal on some cheap ones is super thin and soft, and won't hold a crimp.
All the crimps should pass a good pull test.
There were a few places we crimped and soldered the connection, but those were mainly where water could get to the connectors which are not a water proof type connector.
Being a custom harness, we used the Weather-pack sealed connectors in a few places too, which again is a different crimper die which I already had.