You simply have no idea about the cost of the initial infrastructure. Seriously, we tend to see 'simple proposals' for complex projects which are just the result of people not knowing the actual difficulties of a field. Case in point: Lockheed claiming that it can do in half a dozen years a trailer-sized thermonuclear fusion generator while the entirety of the planet's specialists of the field are working for decades to make a prototype the size of a town. To the surprise of noone, that LM project got redesigned, reworked every time they understood a bit more how complex the endeavour is, until they stopped altogether talking about it in the hopes of no longer looking like fools.Exactly right. (I wish I'd said that.) The first one is probably hideously expensive, but once the infrastructure is built, the cost goes down. How much did the Saturn V boosters cost each? How much more would it have been if there'd only been one? And how much less if there'd been hundreds? (Leave off launch cost, which is a separate problem.)
How much of the process can be automated? Both for building the "yard" & building the habitat? I'll bet it's a fair amount. That also brings cost down.
I've seen a proposal to use giant 3-D printers to blt Mars habitats; no reason it can't work in L4/L5... And it's totally automated. Based on "contour crafting" (?), which is already being used to build things.
Automating and optimizing production only makes you go so far, it doesn't make the crazy affordable or realistic.
... have you ever worked in any industry that requires critical standards of safety? You are just here maximizing the points of potential failure while minimizing the failsafes and verification protocols on an infrastructure made of millions of critical points of failure where a few of them being messed up would kill tens of thousands at least.I don't think most workers would be on site. Many would be planetside operating remotely using the same technology proposed for lunar/NEO mining, which would be a mature technology to anyone thinking of building an O'Neill cylinder (which itself would be simply a bigger version of habitats which would already exist and no doubt house the workers which need to be on-site). There wouldn't be more than a 1.5 second lag or so in communications which combined with some sort of AI for simple corrections should be sufficient. This simplifies construction and would get you down to the range of hundreds of billions. Using the example of the Palm Islands, its the difference between if someone had tried to build them a century ago versus today.
If you are working in a car or an aerospace company, please tell me which one it is so I make sure to NEVER put my life in your products' hands, because your ideas remind me a lot of the NASA officials' in the lead-up to the Challenger disaster. Except that you want to push even more failure points.