Go to fedex.com and set up an account for yourself. It only takes about 5 minutes and the savings are significant over walking in to a shipping store and paying retail.
You can get free laser labels from FedEx, but the easiest way is to just stop at local FedEx metal curbside drop off boxes and snatch up a half a dozen of the domestic shipping pouches. Then when it comes time to print the label, you just print it on a standard letter sized piece of paper, fold in half, and tuck in the pouch.
The best packing material to use on x1/9 sized wheels is "expanded polystyrene", IOW sheets of the same stuff they use to make styrofoam coffee cups. A 2 ft by 4ft 1/2" piece is $2.71 at Lowes.
I shipped a set of 13" wheels from Penna to Calif. I scrounged a toilet bowl box from a friend who was in the middle of a bathroom remodel. Lined it with the 1/2" thick styrofoam and also cut down the styrofoam sheets and used them as dividers to separate the wheels so they wouldn't bang against each other. As I recall it was about a 45# shipment, and was about 24" x 16" x 16".
I just tried to get a rate on FedEx.com but it was not working.