The typical asking rate per listing is in the $30's per square foot per year. The Oceanside region is going through a an increase in rates. In the last 3 months, the median rate went up $31 per sqft per year.
Compared to the rest of the San Diego market, the Oceanside submarket has lower rates, so you should have no trouble finding a great deal in this discounted region.
In the last 90 days, 64 listings have been listed, so you'll want to check back regularly for new listings. About 53% of the available space in the Oceanside are subleases, so you might be able to find a shorter term or below market rent. 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 1,500 sqft. Most properties in this region are close to 2 stories. Most buildings in this area were built in 1987 and are Class B.