Not to mention as (I think) Bob Keeney pointed out for cheaper headsets you have to consider the cost of the PC you have to pair it with, etc.
Actually $3500 is not THAT much for a work computer that you’d use all day, all things considered; the question is, would you want the thing on your head / face all day and would the processing power going into all the sensor and spacial handling better be used for other things. My intuition is that once you get past the initial rush of having this fantastic new product that for most use cases, standard keyboard and monitor are perfectly adequate and in fact superior. For some makers / content creators, certain kinds of remote workers, it might be a great and useful thing for frequent but probably not all-day, every-day use.
In time it will become clearer where the tradeoffs are, and there will hopefully be fewer of them.