The typical asking rate per listing is in the $30's per square foot per year. The Ontario submarket is going through a a rise in rates. In the last 3 months, the median rate rose $4 per sqft per year. That's a 15% rise in rent.
Compared to the rest of the Metropolitan Los Angeles market, the Ontario submarket has lower rates, so you should have no trouble finding a great deal in this undervalued submarket.
In the last 90 days, 38 listings have been posted online, which means listings might be leasing quickly. You'll want to be prepared to make an offer immediately. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,500 sqft. Most properties in this area are around 2 stories. Most buildings in this region were built in 2002 and are Class A.