Is mild steel an acceptable material to use over 4130 steel? It seems that the alloy steel has numerous advantages but how much better is it than mild steel? Will the steel bend or deform if I go over a pothole?

It seems that older bikes used mild steel with no problem at all. Being strapped for cash, it would be a great advantage to use mild steel which is about 7x less expensive than the aircraft grade steel.

Any thoughts?