United Airlines is offering discount tickets for flights between San Francisco to Puerto Vallarta, Mexico. The roundtrip price of $312 included all taxes, fees and fuel surcharges and is available at www.united.com, using the flexible dates tab.For example, I found non-stop United flights (operated by TED) for a long weekend getaway between Wednesday July 30th, returning Sunday August 3rd. The fare books into the "L" fare class and must be booked by July 11th, with travel completed by August 31st.