On average, listings lease in the $30's per square foot per year. The Brea submarket is going through a a rise in rates. In the last 3 months, the median rate rose $32 per sqft per year.
Compared to the rest of the Metropolitan Los Angeles market, the Brea region has lower rates, so you should have no trouble finding a great deal in this depreciated submarket.
In the last 90 days, 15 listings have been posted online, which means new listings most likley are going fast. You'll want to be prepared to tour spaces as quick as possible. About 33% of the available leases in the Brea are subleases, so you might be able to snag a great spot on a short term. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
Even though the median size is 26,370 sqft, there are still 0 new listings below 2,000 sqft. Most buildings in this market are close to 2 stories. Most buildings in this area were built in 1985 and are Class B.