You will not get everything you want in one place.
San Diego is almost at Los Angeles rent prices. Long Beach, CA is a little lower having much of what you look for, is still expensive, and has some decent views, but nothing as beautiful as Marin. And crime rate is low.
Austin, TX is getting closer, as a Democrat Liberal city with somewhat lower cost of living, a diverse educated population, and highly rated among people under 30 years old. There are no beaches.
Maybe Corpus Christi Texas. This small city of 324,000 leans Trump supporting at 48.6/47.1 percents with a few percent more in Libertarian. Rent averaging under $1000 per month, and no State Income tax makes it much cheaper than any city mentioned so far with an index of 84.5 against national average 100. There is the Gulf Coast beaches that people enjoy.
Crime rate is above the US National average.
Corpus Christi 55 and 61 violent and property
USA 31.1 and 38.1
San Diego 35 and 34
Long Beach CA 49 and 38
Los Angeles at 44 and 34
Clearly the average crime rates at higher in Corpus Christi, but the lower living cost allows a safer neighborhood choice.
Corpus Christi does have a diverse population.
You do not get the environmental views of Marin, but cost is much lower.
The activities level is far less than NY.
You will not find an ideal place. There are nice areas around Raleigh/Chapel Hill in North Carolina.
Good diversity and housing costs. Weekend drive to the beaches. Very good for job edvncement opportunities. A ice living environment. Many people there are northeast transplants.
In reading your question and finding a balance, Raleigh area is the closest to what you really seek.
Average rent around 1100 a month.
It is a metropolitan area.
36 and 44 on crime is in range, and again, can live in nicer safer area because of lower housing costs overall.
Weather is moderate.
You cannot get EVERYTHING, but I think you should look closely at your job opportunities in the Raleigh, NC area.
Zillow has 181 results at $750 to $1000 as 1 bedroom minimum
Austin has 324
Long Beach, CA has 4 small units
San Diego shows 3 tiny apartments smaller than a hotel room.