Depends on whether it's a Class I or Class II GBC.
A Class II (offshore company) tends to cost around 2-4,000 USD first year and about the same in annual fees. I would be hesitant about anyone offering it cheaper than that, but it is certainly possible to find.
Class II GBCs don't require any local presence, so if you are talking about Class I, the fees are significantly higher and harder to predict as they tend to be a bit more of a uniquely tailored setup.