I made a wooden box and assembled it right in the parking lot of the FedEx store by my house!! I shipped 5 sbp 14" wheels from Michigan to Pennsylvania for $65.
I've shipped mounted tires/wheels by FedEx ground by putting cardboard circles over the wheels front and back and taping or shrink wrapping them on. You can probably put two together in that fashion. I've heard Greyhound is cheaper but there is no station around me.