Our current estimate is $20 million for the entire town.
PG&E informed us in 2011 that we would get a "betterment" rebate from them when their old overhead system was replaced by a new underground system in any large (20B) project. The size of the rebate is based on their budgetary cost of a brand new overhead system, minus the book (depreciated) value of the system we replaced. Our PG&E representative (Sindy Mikkelsen) told us this rebate could range from a low of 30% to 50% or more of our total project cost; in recent PG&E undergrounding projects in Carmel, Belvedere and Pebble Beach (study), the rebate has been about 50% of the cost. This was new and exciting news, and provides a significant cost reduction.
The original estimate received from R.W. Beck in 2004 was $52M for a town-wide project; as noted above this did not include any rebate from PG&E, and the final cost of our two pilot projects was lower than their bid: $130 per foot instead of Beck's figure of $164 per foot.
We believe a town wide project will provide significant economies of scale over our two small pilot projects. Furthermore, we see no reason why we should not be able to come close to Palo Alto's actual costs on a town-wide project (note that Palo Alto expressed some interest in bidding on our town-wide project if we got to that stage).
So we can reasonably hope for a cost at or below $100 per foot, across our 60 miles of lines. Adding a 40% rebate from PG&E, we arrive at our estimate of the total cost for undergrounding our town of $20M.