yeah, its a big range, depending on if most of that stuff is already in place - in which case it has (mostly) already been paid for.
As for the target audience, i think it is people who want a building within a few days.
As I mentioned, I looked at a number of similar systems myself (we have a number of providers of modular or flat-pack buildings in Europe).
I decided against modular, and had a custom built 6x12m 1.5-story log-build. The pricing was similar - but it took months to complete.
$5k to $50k is a big range. In the video on the article about Musk's unit[1] they state they're initially targeting Accessory Dwelling Units, and specifically California's recently relaxed laws regarding them. I'm not sure the laws specifically regarding those (but there's info here[2]), but I suspect it's a lot cheaper when you're allowed to hook up to the existing house's sewer and power.
It may well be closer to $100k all said and done for a unit not set up as an ADU, but I suspect that the answer to the original question (of who this targets) is "not the people that need to pay $50k in install fees, at least not initially".
1: https://www.teslarati.com/elon-musk-50k-house-texas-pictures...
2: https://www.hcd.ca.gov/policy-research/accessorydwellingunit...