The typical asking rate per listing is in the $30's per square foot per year. The Montebello region is going through a an increase in rates. In the last 3 months, the median rate rose $36 per sqft per year.
Compared to the rest of the Metropolitan Los Angeles market, the Montebello region has more expensive rates, and you'll have to negotiate above asking rent to be in this hot submarket.
In the last 90 days, 7 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 available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,250 sqft. Most buildings in this area are close to 2 stories. Most buildings in this area were built in 1978 and are Class A.