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 new listings most likley are going fast. You'll want to be prepared to make an offer immediately. About 117% of the available space in the Diamond Bar are subleases, so you might be able to snag a great spot on a short term. 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 2,270 sqft. Most properties in this area are around 2 stories. Most buildings in this area were built in 1987 and are Class B.