What is the Stargate cross-chain fee?

Could you please clarify what exactly is the Stargate cross-chain fee? Is it a transactional fee charged for transferring assets between different blockchains using the Stargate protocol? If so, how does it compare to other cross-chain solutions in terms of cost-effectiveness and efficiency? Additionally, are there any specific factors that determine the amount of this fee, such as the size of the transaction or the congestion on the blockchain?