Cost is a relative term. What is your time worth? Hobbyist or commercial time?
Assuming that you have a cabinet that they fit, the AZs can be installed in a couple of minutes.
Building the drawers takes some time. How much depends on the style.
The 3/4" ply slabs with a front edge (like mine) only take a little bit of time, but it is more than just installing the pre-made units.
Slabs with holes for the feet take time to make a template too, but less material.
If it is purely about cash outlay, making them yourself is cheaper, especially if you have some scrap available. If time matters, the AZ might be a better option.
I went with making my own for a couple of reasons. Mine are 20" deep, which leaves space behind them to store accessories or consumables that don't fit in the Systainers themselves. I also knew that they would be expanding over time and I could keep the cost down by using off-cuts of both the plywood and the oak fronts.
Yes, there are a few of us out there with a lot invested in this stuff. Mine may not be 30k, but it's probably close. I only have 2 Systainers that were purchased empty. One is full of router bits and the other is the one with a drawer in the bottom. I store bags of Dominos in the top and spare bits in the drawer. All of the rest are Festool, WoodPeckers, or Shaper. I haven't counted lately, 25 or so?