Most listings are 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 increased $17 per sqft per year.
In the last 90 days, 32 listings have come on the market, which means spaces most likley are leasing quickly. You'll want to be prepared to make an offer immediately. About 44% of the available space in the Orange County are subleases, so you might be able to find a shorter term or below market rent. 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 2,000 sqft. Most properties in this region are around 2 stories. Most buildings in this region were built in 1985 and are Class A.