Remove required field in Grant Application
I don't think there is a non-coding way to do this. You could try to manipulate the UI with an extension to accept a submission without an amount value. But there may be reasons in the business logic why an amount is required, i.e. you may experience follow-up problems if there are grant records without that value in your database.

So unless this is a serious problem for you, I think your workaround is the best way to go.