Might be possible in some of the beach communities in greater Los Angeles and San Diego, e.g. Belmont Shore in Long Beach.

I'm familiar with Palm Springs. Not sure if it fits your price range since it's popular with snowbirds. Plus, it can get below freezing at night.

Florida is always nice

Also, good music and theatre, too. Especially the music.
We've basically gone up the coast for our Florida vacations -- North Miami, Fort Lauderdale, Boca Raton -- then we went to Delray just for an evening to go to a blues bar there, fell in love with the town and now we've stayed there for the last three visits.
Does your SIL play ukulele? We have friends there who run a great uke group!