On average, listings lease in the $20's per square foot per year. The Fullerton region is going through a a rise in rates. In the last 3 months, the median rate went up $2 per sqft per year. That's a 7% rise in rent.
Compared to the rest of the Metropolitan Los Angeles market, the Fullerton region has lower rates, so you should have no trouble finding a great deal in this depreciated submarket.
In the last 90 days, 14 listings have come on the market, which means new listings might be leasing quickly. You'll want to be prepared to make an offer immediately. About 7% of the available space in the Fullerton are subleases, so you will probably need to consider the implications of signing a direct lease with the building. 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 2,030 sqft. Most buildings in this area are close to 2 stories. Most buildings in this region were built in 1975 and are Class B.