Most listings are in the $0's per square foot per year. The Riverside region is going through a decrease in rates. In the last 3 months, the median rate fell $19 per sqft per year. That's a 100% decline in rent.
In the last 90 days, 4 listings have been listed, which means office spaces most likley are 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 1,400 sqft. Most buildings in this area are approximately 2 floors. Most buildings in this market were built in 1990 and are Class A.