Most listings are in the $30's per square foot per year. The West Covina submarket is going through a a rise in rates. In the last 3 months, the median rate rose $38 per sqft per year.
Compared to the rest of the Metropolitan Los Angeles market, the West Covina region has more expensive rates, and you'll have to negotiate above asking rent to be in this hot region.
In the last 90 days, 42 listings have been listed, so you'll want to check back regularly for new listings. About 26% of the available leases in the West Covina 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 available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 750 sqft. Most properties in this market are close to 3 floors. Most buildings in this market were built in 1980 and are Class B.