The typical asking rate per listing is in the $20's per square foot per year. The El Cajon submarket is experiencing a an increase in rates. In the last 3 months, the median rate rose $11 per sqft per year. That's a 57% rise in rent.
Compared to the rest of the San Diego market, the El Cajon submarket has less expensive rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 15 listings have been listed, which means listings 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 available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,300 sqft. Most properties in this area are close to 2 stories. Most buildings in this area were built in 1978 and are Class C.