Has anybody made a dip tube before? What is the process? I've used tube flare kits before to make brake lines for a car, but the shape of the flare on a corny keg dip tube is much different.
I imagine this would be difficult to do well, as the flange geometry is rather severe.
Cold-flaring a hard stainless tube to that degree is likely to end up with fractures.
Even if you could find a tool to make a usable end, I doubt you could make one cheaper when factoring in the cost of the cost of the tubing and the tool. They are only $15 at my LHBS.