i paid about 3$ a foot for 150 ft. of .120 wall 1.5" DOM (one time 2.80 a ft, one time at 3.11$ a ft)
HREW is way cheaper, and 1.75" .120 wall DOM is way more expensive. 4$ a foot?
why don't you get a tape out and measure and figure out how much tube to start with, and go from there.
id say you'll need at least 140ft so you are looking at 3*140~ 420$ in tube+tax
then you need a bender, and a notcher, a welder, and lots of patience. plus you'll need mounting points like good sliders and a good rear bumper id make those first.