Depends on the service. In general, there are two models: 1) subscription fee (annual or monthly, ~$100 USD) with a per item postage fee (~$1-2 USD), or 2) “per item” processing and postage fees (~$5-10 USD per item). These should be your only costs, but be careful not to leave packages languishing for too long or you’ll start accruing hefty “storage fees” (aka, a fine on being too lazy to check your damn mail). Also ensure the forwarder doesn’t charge for the disposal of junk mail, as entering the US credit card game is guaranteed to attract spam mailers like an animal carcass attracts vultures. Unlike vultures, spam mailers serve no necessary ecological functions. You may also need to factor in the cost at which you value your own time. Some forwarding services will mail directly to your address (which will likely be more expensive), but others may deliver to a local pickup location in your city.