On average, listings lease in the $20's per square foot per year. The Corona region is experiencing a an increase in rates. In the last 3 months, the median rate went up $3 per sqft per year. That's a 13% increase in rent.
Compared to the rest of the Metropolitan Los Angeles market, the Corona submarket has lower rates, so you should have no trouble finding a great deal in this discounted region.
In the last 90 days, 20 listings have come on the market, which means new availabilities 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 available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,050 sqft. Most buildings in this market are approximately 2 stories. Most buildings in this area were built in 2005 and are Class A.