I have bought lots of drop 2&1/2" tubing 3/16" wall anywhere from 4&1/2 to5 feet long . for $5.00 a piece ( female receiver ) and 2x2 tubing 1/4" wall 5 feet long or so for about 5 dollars a piece ( male receiver ) at local steel supplier . they have it often
just buy several pieces and keep them for a future job or to have on hand.
I have made so much using a receiver hitch design, all kinds of things.

I would suggest get in good with local steel supplier. drop by and visit when you don't need anything. and it helps to bring them food sometimes out of the blue. . . heck I have given them watermelons, tomatoes, donut's, Honey, all kinds of things. and I get more than that in return.
just be nice to those guys

I hope this helps