Compared to the rest of the Metropolitan Los Angeles market, the South San Gabriel region has lower rates, so you should have no trouble finding a great deal in this depreciated submarket.
In the last 90 days, 1 listings have come on the market, which means new availabilities 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 2,000 sqft.