On average, listings lease in the $10's per square foot per year. The National City region is going through a decline in rates. In the last 3 months, the median rate fell $10 per sqft per year. That's a 39% decline in rent.
Compared to the rest of the San Diego market, the National City region has lower rates, so you should have no trouble finding a great deal in this undervalued region.
In the last 90 days, 6 listings have been listed, which means listings most likley are leasing quickly. 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.
Even though the median size is 59,040 sqft, there are still 0 new availabilities below 2,000 sqft. Most properties in this market are approximately 1 floors. Most buildings in this area were built in 1974 and are Class B.