I haven't built a frame, however, when I have looked at the costs of frames in the past, in all honesty they haven't been all that expensive. The welding of those parts would be only a small saving in cost. The expense comes from actually buying the tubes and spending the time bending, notching, etc, etc. Even then, a frame still isn't expensive.
Where it begins to get expensive is when you have to purchase all the items to turn that frame into a race vehicle, such as suspension arms, hubs, drive shafts, shocks, fuel tank, steering rack, the thousand little $2 items that add up to big dollars, etc, etc,.
