I just found out that now you get one free withdrawal from BlockFi every month. This is a great news because if you choose to withdraw your bonus right after you get it, you won’t lose anything.
Checking in my Coinbase Pro account, it shows that sending $105 worth of BTC from Coinbase to BlockFi costs only about $0.08 (0.00000135 BTC) in network fee!
So you could send BTC from Coinbase to BlockFi, get your $40 BlockFi bonus, send all your BTC back to Coinbase (or to your wallet) using your free withdrawal credit, and pay only about 8 cents in network fee in the entire process.