I'm not entirely sure what you expect for an answer here. A 357 Magnum what? Is it a Colt, S&W, Desert Eagle? Year? Condition? Upgrades? I could say $20 or i could say $3000, but without any specifics, its impossible to answer your question.
The chrome plated colt python 357 magnum is more than $800.
100-300
100-450 USD
About $600.00
100-300
50-350 usd
A .357 Magnum firearm requires .357 Magnum ammunition.
A .357 Magnum can shoot .38 Special rounds as well as .357 Magnum rounds.
Depends entirely on which 357, and the condition of both guns. Some are worth more, some less.
100-300 USD or so
Whatever the market will bear.
No such model exists. The .357 Magnum cartridge was not put into production until 1935, and Ruger was not established until 1949.