For Shielding and Unshielding, the protocol takes a 0.25% fee per transaction with a shield or unshield. This fee is then collected by the DAO treasury and distributed over time to RAIL stakers in the form of Active Governor Rewards.
The Protocol does not take any fees other than this shield/unshielding fee.
To use RAILGUN, users can pay a Relayer to facilitate their transactions (users can self-relay transactions if they want to save on fees). Relayers charge a % premium of the overall gas price for the transaction and not the transaction amount. Thus, Relayer Fees do not increase with transaction size.
As RAILGUN transactions are gasless (users do not need ETH/MATIC/BNB to send transactions once assets are shielded), Relayer fees also contain the underlying blockchain's gas fee converted to whatever asset users are transacting in. For example, if you are sending DAI on the Ethereum blockchain, then the Relayer Fee (which also contains the blockchain transaction gas fee) is paid entirely in DAI and you do not need to hold/spend ETH in your 0zk address.
Therefore, Relayer Fees vary depending on:
What chain you are using RAILGUN on
Gas price at the time of the transaction
What % of the gas fee Relayers decide to charge as an additional premium
Fees are broadcast across the Waku P2P network and are only charged if users decide to send the transaction and consider the fees to be acceptable. Relayer Fees are up to the individual Relayers themselves, but generally they are 10% of the total gas price added as a premium. This 10% can vary depending on the Relayer configuration and Relayers that set lower fees will naturally receive more transactions.
This creates a competitive fee market for Relayer services as users and the market decide on acceptable fees in real time.