The typical asking rate per listing is in the $10's per square foot per year. The El Cajon region is experiencing a a rise in rates. In the last 3 months, the median rate went up $17 per sqft per year.
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 undervalued region.
In the last 90 days, 16 listings have been made available, which means new listings might be going fast. You'll want to be prepared to make an offer immediately. About 50% of the available space in the El Cajon are subleases, so you might be able to sign a shorter term by taking over a previous lease. 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 2,280 sqft. Most properties in this market are around 2 stories. Most buildings in this area were built in 1977 and are Class B.