Most listings are in the $20's per square foot per year. The Fullerton submarket is seeing a decline in rates. In the last 3 months, the median rate fell $4 per sqft per year. That's a 14% decrease in rent.
Compared to the rest of the Metropolitan Los Angeles market, the Fullerton region has less expensive rates, so you should have no trouble finding a great deal in this discounted region.
In the last 90 days, 17 listings have come on the market, which means office spaces are probably going fast. You'll want to be prepared to make an offer immediately. About 6% of the available space in the Fullerton are subleases, so you will probably need to sign a longer term lease with the landlord directly. 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 1,150 sqft. Most buildings in this area are approximately 2 stories. Most buildings in this region were built in 1975 and are Class B.