Not cheap, but obtainable;

https://ammoseek.com/ammo/357sig 

It can be reloaded too. Starline has brass. It's just a bit more trouble than 9mm to reload.

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Oh I’ve seen it too lately, even at Sportsman’s Warehouse (if you don’t mind getting it thrust in with no spit on their pricing). I should have clarified, I’m just now seeing it advertised sporadically now. 2 years ago it was like hen’s teeth.

AIM or PSA had 50ct boxes or target last month for $39.99 which I was amazed by.

OF target loads

Yes it is. I have been dropping in a 40 caliber barrel, to practice with, so I can conserve the .357 sig.
I am down to 7 boxes of FMJ, but I have just shy of 500 rounds of JHP, in .357 Sig But to put it in perspective, I have 4000 plus rounds of 40 cal FMJ, to practice with. The recoil is damn near identical.
Dave (A.K.A. Homebrew)🍺

You can use the .40 in a 10mm too…..