Air France has $429.23 round trip ticket prices for nonstop flights from San Francisco to Paris departing late March to early May. Star Alliance has similar $430 fares for nonstop flights and Oneworld has $420 fares for one-stop flights.
Air France Light Fares allow free carry-on bags, but $23 for seat assignment and $60 for checked bag each way. Better to pay $45 more each way for seat and checked bag included ticket if you need a checked bag.
Air France San Francisco SFO – Paris CDG – SFO nonstop
United Airlines San Francisco SFO – Paris CDG – SFO nonstop