Most listings are in the $30's per square foot per year. The La Mesa submarket is seeing a a rise in rates. In the last 3 months, the median rate rose $8 per sqft per year. That's a 33% rise in rent.
Compared to the rest of the San Diego market, the La Mesa region has smaller rates, so you should have no trouble finding a great deal in this discounted region.
In the last 90 days, 11 listings have been made available, which means new availabilities most likley are leasing quickly. You'll want to be prepared to make an offer immediately. About 27% of the available leases in the La Mesa are subleases, so you might be able to snag a great spot on a short term. 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 1,370 sqft. Most buildings in this market are close to 2 stories. Most buildings in this area were built in 1979 and are Class C.