The typical asking rate per listing is in the $20's per square foot per year. The Walnut submarket is seeing a an increase in rates. In the last 3 months, the median rate went up $0 per sqft per year. That's a 1% increase in rent.
Compared to the rest of the Metropolitan Los Angeles market, the Walnut submarket has lower rates, so you should have no trouble finding a great deal in this depreciated submarket.
In the last 90 days, 3 listings have come on the market, which means leases 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 available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 800 sqft. Most buildings in this market are around 1 stories. Most buildings in this market were built in 1987.