The chassis shop phone # 1 800 530 9494 is the least expensive I have found for all my tubing. They have been historically economical for shipping charges if cut 10' long and sent truck in a round tube. They are open 9.00 AM to 5.00 PM eastern std time. I recommend giving them a call prior to purchasing from another. They can tell you the cost for shipping before you purchase. My catalog shows if you purchase 3 to 4 full lengths which are between 19' and 21' per is $6.36 per foot plus shipping.
If you can use chromoly 1.5/8" .083 wall then it is only $3.00 per foot for the same 3 to 4 full length quantity. Mild steel is more expensive with thicker wall.