On average, listings lease in the $20's per square foot per year. The Glendora region is going through a a rise in rates. In the last 3 months, the median rate rose $6 per sqft per year. That's a 35% increase in rent.
Compared to the rest of the Metropolitan Los Angeles market, the Glendora submarket has lower rates, so you should have no trouble finding a great deal in this undervalued region.
In the last 90 days, 4 listings have been listed, which means leases most likley are going fast. You'll want to be prepared to make an offer immediately. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 630 sqft. Most buildings in this area are approximately 2 floors. Most buildings in this market were built in 1985 and are Class B.
Not much of the real estate is used for commercial space, so it might be hard to find office space. Waste services is the dominant industry in this area. Most of the occupants of Glendora 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.