On average, listings lease in the $20's per square foot per year. The Oceanside submarket is going through a a boost in rates. In the last 3 months, the median rate increased $4 per sqft per year. That's a 16% rise in rent.
Compared to the rest of the San Diego market, the Oceanside region 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 posted online, which means office spaces might be leasing quickly. 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 1,790 sqft. Most properties in this region are around 2 floors. Most buildings in this market were built in 1984 and are Class B.