We believe the cost in our town would be approximately $100 per foot, prior to rebates (see below).
Cost estimates for undergrounding (on a cost per foot basis) vary tremendously due to many factors; it is difficult to get good data that is relevant to our town. This was the primary motivation for the bid we requested from R.W. Beck in 2004 and our two pilot projects in 2008. The bid from R.W. Beck in 2004 worked out to $164 per foot. The final cost of our two small pilot projects was $130 per foot (ref: R.Chiu email on "UG costs" dated 11/19/08). Some recent estimates from a neighborhood effort on La Cresta are closer to $250 per foot. None of these figures include a "betterment" rebate from PG&E (see below).
In terms of large scale undergrounding projects, our neighbor Palo Alto has some of the best data, although they have more sidewalks and streetlights than Los Altos Hills, which would normally indicate our costs should be lower. They are about halfway done with their long term project to bury all their wires. In 2004 they told our committee their current cost was $90 per foot, and this figure was steadily decreasing as (1) they gained experience and (2) horizontal boring (used to avoid disrupting roads and landscapes) costs declined.
At that time Palo Alto told us they hoped to eventually get costs down to $50 per foot.