I’ve shipped a number of frames in the past year all less than $50. 25” x 39” x 8” or 24” x 38” x 8” appears to be the ideal size before shipping rates go up significantly.

https://jensonbikeshipping.com/

Jesnonusa shipping is usually $10 or more less than PirateShip, the final price will be a few dollars more than the quote but for me it’s come out the cheapest.

I also shipped 75% of a complete bicycle using the popular auction website and with fees the total was just under $35, but that requires coordination and a willing participant on the other end.