Uses the existing osC COD functionality. Adds an Order total value on the final checkout page.
To simplify this module, it uses a single flat fee for all destinations and shipping methods. This is the way Canada Post does it, and likely many others. Set a Tax class to the COD fee to add tax onto it.
Based on the loworderfee module, and other modules I've found, that just didn't quite work the way they were supposed to.