Mail-in voters: don't worry about how much postage to use

Put a regular stamp or two on it and mail it at least a couple of business days before June 7th.  

On May 19th 2016 I called the registrar of voters' office to ask what would happen if someone mailed in their ballot with insufficient postage: they replied "It would be taken care of.".  See this article from 2008 

The Alameda County Registrar Office will be charged for the postage due by the Post Office.  One more reason to implement internet voting.