The typical asking rate per listing is in the $10's per square foot per year. The Imperial Beach region is going through a an increase in rates. In the last 3 months, the median rate rose $18 per sqft per year. That's a Inf% rise in rent.
Compared to the rest of the San Diego market, the Imperial Beach submarket has less expensive rates, so you should have no trouble finding a great deal in this discounted submarket.
In the last 90 days, 2 listings have been posted online, which means new availabilities are probably going fast. You'll want to be prepared to tour spaces as quick as possible. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 780 sqft. Most buildings in this region were built in 1990 and are Class A.