Figure $6,000-$15,000 a year for a real small operation: $1M general liability at $2,000-$5,000/yr (classified for land clearing specifically — a landscaping-rated policy may not cover the work), inland marine on the machine at roughly 1-3% of its value per year, commercial auto for the truck and trailer, and workers' comp once you have employees. Municipal bids commonly require $3M via an umbrella.
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