If I was in your situation, I would buy the $19 cable directly from Apple, have it delivered to my house (or pick it up at the Apple Store), and put that new cable in the Mac's box to ensure you are returning it with a working OEM charge cord. This would not only ensure you are returning the system as it should be, but also avoid risking being charged a substantially higher amount or having the return refused, which Apple would be completely within their right to do.