Most listings are in the $10's per square foot per year. The Orange County region is experiencing a a rise in rates. In the last 3 months, the median rate rose $13 per sqft per year. That's a Inf% increase in rent.
In the last 90 days, 3 listings have come on the market, which means new listings are probably 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.
The standard measurement for office space in this area is around 1,000 sqft. Most buildings in this market were built in 1998 and are Class B.