On average, listings lease in the $30's per square foot per year. The San Dimas region is going through a a rise in rates. In the last 3 months, the median rate increased $11 per sqft per year. That's a 45% rise in rent.
Compared to the rest of the Metropolitan Los Angeles market, the San Dimas region has lower rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 25 listings have been posted online, which means leases most likley are going fast. You'll want to be prepared to make an offer immediately. About 8% of the available space in the San Dimas are subleases, so you will probably need to sign a longer term lease with the landlord directly. 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 4,160 sqft, there are still 0 office spaces below 2,000 sqft. Most properties in this region are close to 2 stories. Most buildings in this area were built in 1988 and are Class B.
Not much of the real estate is used for commercial space, so it might be hard to find office space. Utilities is the dominant industry in this area. Most of the folk of San Dimas work from home. Commuting between 30 and 45 minutes a day is the norm for those who opt to reside in this part of town.