Most listings are in the $20's per square foot per year. The Westminster submarket is going through a a rise in rates. In the last 3 months, the median rate rose $27 per sqft per year. That's a Inf% increase in rent.
Compared to the rest of the Metropolitan Los Angeles market, the Westminster submarket has lower rates, so you should have no trouble finding a great deal in this undervalued submarket.
In the last 90 days, 4 listings have come on the market, which means office spaces most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,800 sqft. Most buildings in this area are close to 1 stories. Most buildings in this area were built in 1981 and are Class B.