Hard to understate just how expensive. Here in Montreal where ice storms kill and cause billions in damage, we still don't bury the main transmission lines. We been burying almost everything _in_ the city where having to repair millions of individual connections (again) would be impractical, but it's relatively simple to repair the limited major lines into the city.

From CBC:

> Current estimates are that it would cost five to 10 times more to distribute electricity to a big city via underground cables, and that not all of nature's problems would be alleviated even if that were done.

Horizontal directional drilling costs $10 to $30 (USD) per linear foot with upfront fixed costs of $30K or so.

How does that compare to building above ground towers to support cable weight in all conditions?

I'd assume / guesstimate that route planning, community advisement, actual cable length, etc. costs are more or less the same in either case.