The typical asking rate per listing is in the $20's per square foot per year. The Santa Ana region is going through a decline in rates. In the last 3 months, the median rate fell $1 per sqft per year. That's a 2% decrease in rent.
Compared to the rest of the Metropolitan Los Angeles market, the Santa Ana region has less expensive rates, so you should have no trouble finding a great deal in this depreciated submarket.
In the last 90 days, 129 listings have been listed, so you'll want to check back regularly for new listings. About 5% of the available leases in the Santa Ana are subleases, so you will probably have to consider a longer term lease. 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 2,000 sqft. Most buildings in this market are around 2 stories. Most buildings in this area were built in 1982 and are Class B.