Shooting .357 Magnum is no cheaper than shooting .357sig,
if you check online prices.
If I was a hunter perhaps I'd prefer the Magnum, but purely for personal self-defense I'll take my 13+1 G-32. And I still believe there's great opportunity for ammo companies to introduce 130-150 grain rounds in the sig caliber. Sellier & Bellot already offers a great 140-grain truncated cone round that I carry for the rare times I'm in the woods.