On average, listings lease in the $20's per square foot per year. The Barstow region is going through a an increase in rates. In the last 3 months, the median rate rose $24 per sqft per year. That's a Inf% rise in rent.
Compared to the rest of the Metropolitan Los Angeles market, the Barstow region has lower rates, so you should have no trouble finding a great deal in this undervalued submarket.
In the last 90 days, 5 listings have been made available, which means listings most likley are going fast. You'll want to be prepared to make an offer immediately. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,600 sqft. Most properties in this region are around 2 stories. Most buildings in this market were built in 1970 and are Class B.