On average, listings lease in the $10's per square foot per year. The Fontana submarket is going through a decline in rates. In the last 3 months, the median rate fell $14 per sqft per year. That's a 51% decrease in rent.
Compared to the rest of the Metropolitan Los Angeles market, the Fontana submarket has lower rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 10 listings have been made available, 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 on the market, so finding a space for a small business might be tough.
Even though the median size is 6,350 sqft, there are still 0 leases below 2,000 sqft. Most properties in this market are around 2 floors. Most buildings in this area were built in 1991 and are Class A.