You don't have to cancel the Instant Deposit feature to avoid instant deposits and paying the extra fee. All you need to do is turn off the scheduling of them:
Select the gear icon > Accounts and Settings > Payments tab on the left > Deposit Speed > Set a schedule for instant deposit > Click the "All Days" checkbox to toggle all days to "Off".
Now, when a deposit becomes available, you should be prompted to mark it for Instant Deposit, or not.
