On average, listings lease in the $30's per square foot per year. The Downey region 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 region has lower rates, so you should have no trouble finding a great deal in this discounted region.
In the last 90 days, 1 listings have been listed, which means new 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 780 sqft. Most properties in this region are approximately 2 stories. Most buildings in this region were built in 1968 and are Class B.