United Airlines have $28 OW or $56 RT airfares travelling to and from San Francisco (SFO) and Las Vegas (LAS). This is nonstop service. There are several flights daily and multiple flights on these dates will apply.
Travel availability:
Depart SFO: April 25, 26; May 2, 3, 9, 16, 23, 31
Depart LAS:: May 3, 17
Use the dates above and plug dates into Priceline , Orbitz , CheapOAir , Expedia or United Airlines directly
See sample travel itinerary from Priceline