The cost of general liability depends on.
1) The type of contracting work you plan to do (Commercial, Residential, Demolion etc).
2) The amount of work you plan to perform in a year.
3) Your expected payroll and/or subcontractor expenses.
4) The amount of coverage you want.
(Do you want $100,000, $500,000 or $2,000,000 in coverage)
A $ 500,000 policy can cost one contractor $5,000 and another $8,000. I recommend getting a few quotes from an insurance agent that specializes in writing policys for general contractors.