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.
About $600.00
100-300
50-350 usd
100-300
100-450 USD
Depends entirely on which 357, and the condition of both guns. Some are worth more, some less.
No such model exists. The .357 Magnum cartridge was not put into production until 1935, and Ruger was not established until 1949.
Whatever the market will bear.
100-300 USD or so
No, there are .357 caliber bullets that are not magnum, but they are in the minority.
100-5000 USD depending on EXACTLY what you have.