I have been able to book a rental car thru expedia, in the past, with a drop at a different location

Southwest Airlines is likely your best option for One Way Flights. If you use expedia you pay a service charge($7) for all airlines booked with them. So, just book directly with the airlines if using American, Delta, or United.
There are other small companies that probably fly from Vegas, San Fran, and LA. You might also want to check the cost to San Jose and Oakland, as sometimes you can save a few dollars and they not from from SFO anyway.
I have been able to book a rental car thru expedia, in the past, with a drop at a different location. Again, you might be better off renting the car in San Jose or Oakland. You just have to do a lot of research to find the best price.
Actually the $7 fee only applies if you're booking a flight using two different airlines (for example, NY-LAX roundtrip flying united one way and then delta on the return.) Since that won't apply in your case, I'd still check expedia to get an idea of fare. While I still prefer to book directly with the airline whenever possible, expedia or one of the other sites is a good place to get an idea of fares. You can always then go to the airline website.
Just as a side note, for multiple legs, sometimes expedia can offer combinations the airline won't (I just bought a mult-city United ticket with times the United website didn't show and that I couldn't even get by calling.)
Fly to LV and rent a much cheaper rental car and see southern hotels in downtown seattle wa NV and southern California and return the car to Las Vegas and then fly to Oakland and rent another car there if you need one to see what you want in the SF area.