$250 - Weekend Flight to Boston from San Francisco on Virgin America
Virgin America offers one-way flights between Boston and San Francisco for $119. The big caveat is that you need to book your flight at least a few weeks ahead of time. In some cases, you need to book two to three months ahead of time.
I’ve found roundtrip nonstop flights between Boston and San Francisco for $250 including taxes and fees with Virgin. Flight leave San Francisco just after 10 on Friday, and come back in the afternoon on Sunday.
You could also fly to Boston on a Thursday and fly back on a Monday, and pay the same price, but not need to book your flight quite as far in advance.