Most listings are in the $20's per square foot per year. The National City region is seeing a decrease in rates. In the last 3 months, the median rate fell $3 per sqft per year. That's a 8% decrease in rent.
Compared to the rest of the San Diego market, the National City submarket has less expensive rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 5 listings have been listed, which means spaces might be leasing quickly. You'll want to be prepared to make an offer immediately. About 280% of the available space in the National City 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 posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 990 sqft. Most buildings in this region are around 1 floors. Most buildings in this market were built in 1974 and are Class B.