Unicorn; just an FYI. The ammo cost for the mosin and the 357 are almost identical. Actually; except for mil-surplus, the lever action is actually CHEAPER on ammo.
See; the 357 magnum can also shoot 38 special. A box of 50, 158 grain, 38spl, costs about $14 online. Cheaper in bulk. That's $0.28 per round, or $5.60 for a box of 20. Again, that's $14 per box NOT IN BULK. 7.62x54 NOT IN BULK, will cost about $9 for a box of 20. In bulk; mil-surplus; it's around $4.80 a box of 20. So, as you see, 38spl and mosin ammo is almost identical. In many cases, the 38spl is cheaper. And definitely easier to find locally.
Now, there is no doubt that mil-surplus mosin rifles are cheaper. You can get them as cheap at around $100-$125. The 357 magnum lever is going to cost around $350 used and around $500 new. But you have to decide what you're going to do with the rifle.
1. Ammo: Already showed that the price of the two is almost identical
2. 357 mag lever: Can hunt deer and small game, fun to plink with.
3. Mosin: Can hunt deer; too much for small game, not much for plinking because it's a full rifle round and recoil. Not bad; just not like a 357/38.
4. Home defense: The 357 lever is better. More rounds; better defense ammo available; easier to find ammo; no real recoil.
So, it depends. Yes, the rifle is cheaper in the mosin, but NOT the ammo. Plus, you have a lot more versatility with the 357 lever.