The typical asking rate per listing is in the $30's per square foot per year. The Diamond Bar region is experiencing a an increase in rates. In the last 3 months, the median rate went up $39 per sqft per year.
Compared to the rest of the Metropolitan Los Angeles market, the Diamond Bar submarket has more expensive rates, and you'll have to negotiate above asking rent to be in this hot region.
In the last 90 days, 21 listings have been posted online, which means new listings are probably going fast. You'll want to be prepared to make an offer immediately. About 5% of the listings in the Diamond Bar are subleases, so you will probably need to consider the implications of signing a direct lease with the building. 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 1,820 sqft. Most properties in this region are around 2 stories. Most buildings in this market were built in 1987 and are Class B.