On average, listings lease in the $20's per square foot per year. The River Edge region is going through a an increase in rates. In the last 3 months, the median rate rose $24 per sqft per year.
In the last 90 days, 1 listings have come on the market, 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 on the market, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,000 sqft. Most properties in this region are around 2 stories. Most buildings in this market were built in 1983 and are Class A.