Fly nonstop from New York JFK to Ontario, CA for $197 round-trip or vice-versa on JetBlue. This city-pair is one of the newly announced routes that JetBlue will be flying starting in early September. You can see a full list of new routes and some information on JetBlue's push into new Western markets here.
This particular fare is available from September 5 through November 7, 2018, with travel days valid on Tuesday, Wednesday, and Saturday at this price. The best way to find this flight as it's not currently listed on many third-party booking sites is to book directly via JetBlue's homepage. Searching there, I could see seats available departing JFK on Saturday, September 8, and returning from ONT on Saturday, September 15, 2018.
Need a place stay in the Ontario area? Here's a list of stylish accommodations available for the mentioned travel dates on Hotelwatchdog.