This is my 2 cents.
I think sometimes we are blind to the total economics. For example I think most of the parts in the Atomic 1st stage kit are rather simple, so I'll make my own kit. I believe the o-rings (8 i think) are standard size, after I spend a day soucing and figuring out what durometer to buy I pull the trigger. However, I have to by in bulk so I end up with enough o-rings for 100 kits that cost me ~ $100 with tax and shipping and i still don't have the specialty parts such as the high pressure seat, filter, and teflon washer and spring clip. Ok simple piece of teflon machined for the HP seat. I'll make one. Some $1000 later after I engineered what material and got the tooling I can make them for $1.00 each if I make 100. Spring clip filter and teflon washer I get a deal on and by 100 for another $500. Then of course I have to package (bags $30) and store them until I can distribute them to my friends. My cost overall cost per kit is probably $7. So I think cool, and I brag to my friends how cheap I can get a kit, and I will sell them one. 10 years later I still have enough for 80 more regulators. My labor and warehousing cost are not factored in because I am doing this in my free time and my garage is attached to my house. Manufactures don't have this luxury they pay for labor, warehousing, inventory tax, tax on profits, insurance, marketing, etc. In reality the cost of my first kit was probably $2000-3000 if i factor in a cost of labor for time and the materials, not to mention long term storage. So at this stage the $40 i pay for the kit is worth it, as long as I can get the kits. It is a different story if the manufacturer restricts the parts. Then we start going down the path of Right to Repair ( Google Apple or John Deer and RIght to Repair).