The typical asking rate per listing is in the $20's per square foot per year. The Mission Viejo region is going through a an increase in rates. In the last 3 months, the median rate went up $27 per sqft per year.
Compared to the rest of the Metropolitan Los Angeles market, the Mission Viejo submarket has smaller rates, so you should have no trouble finding a great deal in this undervalued region.
In the last 90 days, 14 listings have been listed, which means leases most likley are going fast. You'll want to be prepared to tour spaces as quick as possible. About 129% of the office spaces in the Mission Viejo 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 posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,500 sqft. Most buildings in this region are approximately 2 floors. Most buildings in this market were built in 1988 and are Class B.