Most listings are in the $30's per square foot per year. The National City region is going through a an increase in rates. In the last 3 months, the median rate increased $7 per sqft per year. That's a 30% rise 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 discounted submarket.
In the last 90 days, 5 listings have come on the market, which means listings might be leasing quickly. You'll want to be prepared to make an offer immediately. 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 1,010 sqft. Most buildings in this region are around 2 stories. Most buildings in this region were built in 1974 and are Class B.