The typical asking rate per listing is in the $20's per square foot per year. The Fountain Valley region is going through a a rise in rates. In the last 3 months, the median rate went up $21 per sqft per year.
Compared to the rest of the Metropolitan Los Angeles market, the Fountain Valley region has lower rates, so you should have no trouble finding a great deal in this discounted region.
In the last 90 days, 13 listings have been posted online, which means listings most likley are leasing quickly. You'll want to be prepared to make an offer immediately. About 31% of the available leases in the Fountain Valley 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 2,400 sqft. Most properties in this region are close to 3 floors. Most buildings in this region were built in 1983 and are Class B.