Oh I thought you where referring to some extra cost related to buying stellar itself to get into the airdrop. Well I dont use webull so I cant help you there. As far as Coinbase goes, I dont pay any fee to deposit money. Just goto pro.coinbase.com (same login info as you use for coinbase.com) and deposit USD from there, its free and you pay WAY less fees on exchanges from pro.coinbase.com then you do on coinbase.com

Your cost should be around $0.70 in exchange fee per 500 xlm that you purchase and thats all the cost you should incur. Free deposit, free transfer of xlm from Coinbase to your stellar wallet and zero exchange fee to trade .05 xlm for 1 aqua on the stellar dex in your stellar wallet since their are no fees for any trading on the stellar exchange.

As you see my fee is $0.50 to buy 500 xlm but its discounted for me based on how much money I've traded on pro.coinbase.com in last 30 days.

Note: You will be able to trade the money you deposit instantly on pro.coinbase.com possibly depending on where you live but you wont be able to withdraw any of it for 7 days until the ACH transaction clears with the bank which is fine since you have until Jan. 14th to move the xlm to the xlm wallet and buy 1 aqua