Most listings are in the $20's per square foot per year. The Glendora region is seeing a decline in rates. In the last 3 months, the median rate fell $2 per sqft per year. That's a 9% decline in rent.
Compared to the rest of the Metropolitan Los Angeles market, the Glendora region has lower rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 7 listings have come on the market, which means listings most likley are going fast. You'll want to be prepared to make an offer immediately. About 86% of the available leases in the Glendora 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 1,500 sqft. Most properties in this market are around 2 floors. Most buildings in this market were built in 1985 and are Class B.