The typical asking rate per listing is in the $10's per square foot per year. The Bostonia submarket is going through a a boost in rates. In the last 3 months, the median rate went up $16 per sqft per year.
Compared to the rest of the San Diego market, the Bostonia submarket has smaller rates, so you should have no trouble finding a great deal in this discounted region.
In the last 90 days, 2 listings have been made available, which means new availabilities most likley are going fast. You'll want to be prepared to make an offer immediately. 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 800 sqft. Most buildings in this area are close to 2 floors.