In my opinion you would need more than just a soldering iron and some basic skills to execute this cable properly!
First of all you have about $120-$150 in parts, depending on where you get them. Time needed to source the parts, minimum 2 hours if you know where to go. Second, there are number of tools you will need to pull this off. Some you might have, some you probably will not. There are also various supplies you will need, such as different sizes heat shrink, cables sleeving etc. Now! You have 13 connectors (if you want a quick connect on both sides) 4 of those are multi pin (7 contacts, possibly . You have at least an hour or two of cable preparation, measuring, cutting, stripping and tinning. Once that's completed, all that is left to do is solder the connectors, another hour or two, depending on your level of expertise. When you add it all up it turns out to be something like 6 hours of work + $150 in parts, that is best case scenario, IF everything goes as planned. You would have to be a very good cable maker to pull it off for the same price that you can get it at Trew, unless you are making a batch of 100. All I'm saying is that even though the price feels "pretty ridiculous" to you, it's actually pretty fair.
Now! I am all for sound guys making our own cables, repairing our gear and developing our skills. Great amounts of pleasure and pride comes from that, we all love doing it for those reasons, however, the above statement sounds a lot like something I would hear from a producer or a director who says:
We don't need a sound guy, we have an onboard mic! With a furry!