Most listings are in the $30's per square foot per year. The Brea region is going through a a boost 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 undervalued region.
In the last 90 days, 15 listings have come on the market, which means listings are probably going fast. You'll want to be prepared to make an offer immediately. About 33% of the available leases in the Brea are subleases, so you might be able to sign a shorter term by taking over a previous lease. There aren't many listings below 2,000 square feet available, 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 availabilities below 2,000 sqft. Most properties in this market are around 2 floors. Most buildings in this region were built in 1985 and are Class B.