A quick distinction, you have to build all of a skyscraper but you only get to sell part of it as condos. There are hallways, janitors' closets, fire stairways, etc etc.

Yes, this exactly. If you can get 70% efficiency in a skyscraper you're doing phenomenally well. Also, the cost of land isn't included in the $300/sq.ft. number (though that becomes a proportionately smaller concern for taller buildings, for obvious reasons), nor the costs of financing, insurance, maintenance, etc.

But more to the point, these numbers set only the lower bound on what a unit will sell for. These numbers don't predict the final market price of new construction, but they tell you when a project can be justified.

Hmm, [1] suggests 25% overhead for 30-40 stories.

Maintenance is largely irrelevant to the sales price, assuming the HOA/condo association fees aren't wildly out of line with others. Also, these should scale linearly or sub-linearly I'd think.

I still don't see an answer to why $300/ft2 (or hell, $500/ft2) construction costs are a problem when condos sell for $1k +- 50 ft2 in the north east chunk of sf. Even $500/0.70 = $714 / salable ft2. Which should make selling prices near $1k a damn attractive proposition.

The cost of land goes as

   (land cost / ft2) / ((1/0.7) x (stories - 1))

so even $5k/ft2 of land cost comes out to $103 per salable ft2 on a 35 story building.

[1] https://westnorth.com/2015/04/27/high-rises-land-efficient-b...

Replying to self: denominator on land costs should have factor .7 not (1/.7) so $210. Embarrassed.