On average, listings lease in the $10's per square foot per year. The Orange County region is going through a a boost in rates. In the last 3 months, the median rate rose $1 per sqft per year. That's a 11% increase in rent.
In the last 90 days, 25 listings have been listed, 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 1,030 sqft. Most buildings in this region were built in 1998 and are Class B.