Compared to the rest of the Metropolitan Los Angeles market, the Diamond Bar region has more expensive rates, and you'll have to negotiate above asking rent to be in this hot submarket.
In the last 90 days, 23 listings have been listed, which means spaces most likley are going fast. You'll want to be prepared to tour spaces as quick as possible. About 4% of the available space in the Diamond Bar are subleases, so you will probably have to consider a longer term lease. There aren't many listings below 2,000 square feet on the market, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,840 sqft. Most buildings in this region are approximately 2 stories. Most buildings in this market were built in 1987 and are Class B.