Most listings are in the $20's per square foot per year. The Walnut region is seeing a an increase in rates. In the last 3 months, the median rate increased $23 per sqft per year. That's a Inf% rise in rent.
Compared to the rest of the Metropolitan Los Angeles market, the Walnut submarket has less expensive rates, so you should have no trouble finding a great deal in this discounted submarket.
In the last 90 days, 1 listings have been listed, which means listings most likley are going fast. 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 960 sqft. Most buildings in this region were built in 1987.