The typical asking rate per listing is in the $20's per square foot per year. The San Marcos submarket is going through a a boost in rates. In the last 3 months, the median rate went up $5 per sqft per year. That's a 21% increase in rent.
Compared to the rest of the San Diego market, the San Marcos region has less expensive rates, so you should have no trouble finding a great deal in this undervalued region.
In the last 90 days, 114 listings have come on the market, so you'll want to check back regularly for new listings. 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 1,680 sqft. Most properties in this market are around 2 stories. Most buildings in this market were built in 1984 and are Class B.