I was searching in fabrication processes and get ideas want to share here regarding making a spears ,cost will be from labor charges only and not from materials here the way I think its how they do ,may be there is some tricks but the idea is same
get either 17-4 or 15-5 alloy in normal condition
weld or machine what you want on it
straightness the bar within the tolerance ranges
heat treat your spear in the accurate temperature (u search for it )
get your spear ready
is it simple like that ?