Why are fees in Ethereum network so high?
When transactions deal with the Ethereum blockchain (sent TO/FROM the Ethereum network), there's an Ethereum miners’ fee. It cannot be avoided, but it is paid only once during a transaction on the Ethereum blockchain.
We (Aurora) have no control over (1) the market price of ETH or (2) the congestion of Ethereum, and therefore we have zero control over how much that second transaction will cost you.
Typically, a transfer of ERC-20 to Aurora requires around 70k gas on Ethereum (Approve + Lock). Transferring it back would take around 330k gas to finalize, up to USD300 that is. So transfers back might be more expensive.
The bridge itself doesn’t charge any fees.