Most listings are in the $20's per square foot per year. The Westminster region is going through a an increase in rates. In the last 3 months, the median rate increased $27 per sqft per year. That's a Inf% rise 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 depreciated submarket.
In the last 90 days, 5 listings have been listed, which means listings are probably leasing quickly. You'll want to be prepared to make an offer immediately. There aren't many listings below 2,000 square feet on the market, 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 properties in this market are close to 1 floors. Most buildings in this area were built in 1973 and are Class B.