On average, listings lease in the $30's per square foot per year. The Diamond Bar region is seeing a decrease in rates. In the last 3 months, the median rate fell $6 per sqft per year. That's a 14% decline in rent.
Compared to the rest of the Metropolitan Los Angeles market, the Diamond Bar submarket has lower rates, so you should have no trouble finding a great deal in this depreciated submarket.
In the last 90 days, 23 listings have been listed, which means spaces most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. About 52% of the listings in the Diamond Bar are subleases, so you might be able to find a shorter term or below market rent. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
Even though the median size is 2,630 sqft, there are still 0 new listings below 2,000 sqft. Most properties in this area are close to 2 stories. Most buildings in this area were built in 1987 and are Class B.