The typical asking rate per listing is in the $30's per square foot per year. The Downey submarket is going through a a rise in rates. In the last 3 months, the median rate rose $31 per sqft per year.
Compared to the rest of the Metropolitan Los Angeles market, the Downey submarket has lower rates, so you should have no trouble finding a great deal in this depreciated submarket.
In the last 90 days, 1 listings have come on the market, which means new availabilities are probably 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 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 780 sqft. Most properties in this market are around 2 floors. Most buildings in this area were built in 1968 and are Class B.