High-rise construction is expensive, but high-rises aren't necessary for density. Wood-built low- and mid-rise is far more cost efficient, especially when you don't require 1-2 parking spaces per unit.
The reason why we get too many high-rises and too few low-rises is because of regulatory burden. In particular, the long, drawn-out, and capricious manner in which the laws are administered and challenged. In that kind of environment high-rises become more common simply because of the economy of scale--a high-rise developer has resources and the wherewithal to see the project through where developers of smaller developments do not.
The most important thing for commerce and especially real estate development is consistency and predictability. Proposition 13 and the cost of labor can be dealt because they're known quantities. Zoning boards and CEQA[1] are the real killers as the unpredictability compounds, many fold, the nominal regulatory burden.
[1] Compare NEQA to CEQA. The Federal NEQA law isn't much of an impediment to development anymore because an efficient ecosystem has developed--specialized assessment agencies that do the work quickly and cheaply, and relatively efficient administration of the regulatory regime. The cost of a NEQA impact statement is a known quantity and is easily budgeted. By contrast, under CEQA it's much easier for NIMBYs to challenge impact statements, which means the time and budget required for getting over the CEQA hurdle can be indefinite.