Attention should be paid to the literature the EAA puts out for people welding their own steel aircraft structures, including their reprint of AC 43-13-1B et seq.
If the frames are $1800 commercially and use $300 of steel and would take a hobbyist 40 hrs to fabricate, that's 1500/40= 37.50/hr. If you make $37.51 an hour after tax then from a pure economic standpoint you should buy your frame commercially.
Add in the educational value you get from the welding practice (I forgot to add rod and gas in, unless they are in the steel bill) and subtract the risk factor if your homemade frame breaks.
You'd think someone would have them made in Mexico or something.....shhh, maybe we shouldn't give them any ideas...on second thought if they make them there it will keep the Mexicans home, that's worth something too! I mean I like Mexicans fine...in Mexico that is.