If you decide to take a bike on a plane and fly commercial in USA, last year when I was checking a few prices I found that Southwest was pretty close to reasonable for a bike box. In the left hand column at this link, click on the Sports Equipment button. Then go down the list to Sports Equipment - Special Items to find bicycles. $75. I am not sure but I think that would mean that the bike is one of your two alloted free pieces of checked luggage.
https://www.southwest.com/html/custo...ggage-pol.html
My next trip is on Air Canada. They also have a close to reasonable fee for a bike box, much better than Delta and some of the others.
If you are fortunate enough to be starting and ending near Amtrak stations that handle luggage,
https://www.amtrak.com/express-shipping
I once heard that you can pay REI to ship a bike in a box from one REI store to another but I have never looked into that. Not sure if they still do it or not.