If I'm reading the pricelist at the below link correctly, $0.142 is the lowest rate for standard mail commercial letters weighing 3.3 oz or less; however, a footnote in the chart indicates the mailer can "subtract $0.001 for each letter that complies with the full-service Intelligent Mail option requirements."
I don't know what the Intelligent Mail option requirements are but it seems to imply that one could see a rate of $0.141 on a commercial standard mail letter.
http://pe.usps.com/cpim/ftp/manuals...otice123.pdf