The typical asking rate per listing is in the $30's per square foot per year. The Diamond Bar submarket is going through a a boost in rates. In the last 3 months, the median rate increased $32 per sqft per year.
Compared to the rest of the Metropolitan Los Angeles market, the Diamond Bar region has less expensive rates, so you should have no trouble finding a great deal in this discounted region.
In the last 90 days, 23 listings have been made available, which means new listings most likley are going fast. You'll want to be prepared to tour spaces as quick as possible. About 48% 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 available, so finding a space for a small business might be tough.
Even though the median size is 2,630 sqft, there are still 0 office spaces below 2,000 sqft. Most buildings in this region are close to 2 stories. Most buildings in this area were built in 1987 and are Class B.