I don't believe the large boxes are used boxes. When I picked up one last year it was a new box. Amtrak charges $20, Shiphol Airport 25 Euros, Frankfort Airport 35 Euros. Fifteen dollars might be a bargain.

If your LBS sell e-bikes, ask them for an e-bike box. They are larger than conventional bike boxes. Also bike boxes come in all sizes, ask for the biggest box they have. While your at it ask for some of the protective items the manufacturers use for shipping: fork spacers, derailleur protectors, axle discs.