On average, listings lease in the $20's per square foot per year. The Ontario region is experiencing a a rise in rates. In the last 3 months, the median rate went up $3 per sqft per year. That's a 12% increase in rent.
Compared to the rest of the Metropolitan Los Angeles market, the Ontario submarket has smaller rates, so you should have no trouble finding a great deal in this undervalued region.
In the last 90 days, 48 listings have been made available, so you'll want to check back regularly for new listings. About 2% of the listings in the Ontario are subleases, so you will probably need to consider the implications of signing a direct lease with the building. 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 region are close to 2 floors. Most buildings in this area were built in 2002 and are Class A.