On average, listings lease in the $20's per square foot per year. The National City region is seeing a decline in rates. In the last 3 months, the median rate fell $2 per sqft per year. That's a 9% decrease in rent.
Compared to the rest of the San Diego market, the National City submarket has lower rates, so you should have no trouble finding a great deal in this discounted submarket.
In the last 90 days, 14 listings have been listed, 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 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 830 sqft. Most properties in this region are approximately 3 stories. Most buildings in this area were built in 1974 and are Class B.