This story about Napa County, California considering moving to vote-by-mail for special elections contains this very interesting analysis, in which the county elections registrar explains where the main savings come from:

Essentially, savings come not from the elimination of each individual polling place, but from the fact “that you don’t have to gear up for a polling place election at all,” Tuteur said.

Such “gearing up” efforts include providing the state-mandated electronic voting machines — mainly serving visually impaired voters — at each polling place; the roughly 15,000 sample ballots that must be mailed to polling place voters; and the trucking costs associated with transporting the equipment and ballots to and from the registrar’s office, Tuteur said.

The HAVA mandate that each precinct have at least one accessible machine was predicated on the goal that all visually impaired (and others with disabilities) be able to vote independently.  One consequence of shifting to vbm will certainly undercut the HAVA goals.  I’m quite surprised that Napa is being quite so explicit about this, however.  (In fairness, the connection between electronic voting machines and their use by visually impaired voters may be the reporter’s, but the implications are the same.)