The typical asking rate per listing is in the $30's per square foot per year. The Westminster submarket is going through a an increase in rates. In the last 3 months, the median rate increased $4 per sqft per year. That's a 15% increase in rent.
Compared to the rest of the Metropolitan Los Angeles market, the Westminster submarket has smaller rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 4 listings have been listed, which means listings most likley are leasing quickly. You'll want to be prepared to make an offer immediately. 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 region are approximately 1 stories. Most buildings in this market were built in 1973 and are Class B.