shipping a front seat

If you & buyer are near Greyhound bus stations that is the cheapest way to ship. Check their size & weight limits, you might need to take the seat backs off.
The cost of packing & shipping might be the same as the cost of the seat itself so make sure the buyer is willing to cover it all.
A good source for cardboard boxes is a furniture store and I like the boxes bicycles come in so a bike shop or sporting goods store might also have a good box.
Yes it can be a bit of effort just use a lot of tape.
This might not seem lucrative but it is an important service that helps others keep & enjoy their A-body.