[pjmlp]

UNIX was only cheap because AT&T was forbidden to profit from it, had it not been the case, it would have been a proprietary closed source OS, exactly at similar price points.

The proof being the graphical UNIX workstations from Cray, SGI, Sun, NeXT that came later into the market.

[Pay08]

The dimension you're missing here is that most of the Lisp OSs were single-user (AFAIK initially all of them were but some gained multi-user support later) in a period when timeshare was king. Not to mention that the hardware itself cost multiple times more to manufacture.

[pjmlp]

How many UNIX graphical workstations from Cray, SGI, Sun, NeXT do you think were multiuser in practice?

As for price, they were also not cheap to get.

[jrumbut]

You could probably say the same about any operating system, especially if you exclude the same human user operating in multiple roles.

Though in the Unix environment, additional user accounts and groups that don't actually correspond to separate humans have a lot of pragmatic uses.

[pjmlp]

Yes, however that wasn't a relevant feature for 1980-90's workstation market, like under which user the printer daemon would be running under.