On average, listings lease in the $30's per square foot per year. The Santa Ana region is going through a a boost in rates. In the last 3 months, the median rate increased $6 per sqft per year. That's a 23% increase in rent.
Compared to the rest of the Metropolitan Los Angeles market, the Santa Ana region has lower rates, so you should have no trouble finding a great deal in this depreciated submarket.
In the last 90 days, 143 listings have come on the market, so you'll want to check back regularly for new listings. About 4% of the available space in the Santa Ana 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 on the market, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,150 sqft. Most buildings in this area are around 2 stories. Most buildings in this area were built in 1982 and are Class B.