With as light as a single shaft is, you should be able to ship it via UPS to just about anywhere in the country for around $10. @sdandrea1 mentioned PirateShip, you can use their website to get an idea of costs from your zip code: https://www.pirateship.com/usps/shipping-calculator
As you mentioned boxes aren't cheap, you need to buy in bulk to get a decent price. You can get 1.5" x 48" carboard tubes for about $2/ea in a 50-pack.
And for padding, I use the big-bubble wrap (small bubbles won't protect it very well). I lay down a 48" length and wrap it all the way around the shaft and tape it up. Fills up the tube nicely and protects the shaft pretty well if the box gets crushed. A 2-pack of this stuff will do 50 shafts for $25, so about $0.50/ea.