Most listings are in the $20's per square foot per year. The Orange submarket 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 7% increase in rent.
In the last 90 days, 5 listings have come on the market, which means spaces most likley are going fast. 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 2,100 sqft. Most properties in this market are around 2 floors. Most buildings in this market were built in 1984 and are Class B.