On average, listings lease in the $10's per square foot per year. The Orange County submarket is experiencing a a boost in rates. In the last 3 months, the median rate rose $13 per sqft per year. That's a Inf% rise in rent.
In the last 90 days, 3 listings have come on the market, which means new listings 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 1,000 sqft. Most buildings in this area were built in 1998 and are Class C.