We’re using BitGo’s Enterprise wallet and we are utilizing their integrated algorithm for dynamically applying the optimal amount for transaction fee according to bitcoin network past and present status.
We only cover operating costs and if fees are high this is due to blockchain conditions.
Please note that you can convert BTC to XRP for example and you will greatly reduce the cost of withdrawal.
Also, Coinbase withdrawals are still free and you can use Lightning Network to withdrawal the BTC.
https://www.nicehash.com/support/general-help/nicehash-service/fees