They're not pure silver, they're 90% silver.
If you have common-date 90% silver coins in circulated condition, the price will fluctuate with the precious metals market. Currently, the spot price of silver is somewhere near $14 a troy ounce. At that price, the melt value of a quarter is $2.50, so a dealer should pay about $2 for a pre-65 quarter and sell one for $3. In large quantities ($1000 bags) the prices will be closer to the melt value.
it is worth about 50 dollars
No "quarter silver dollars" have been made by the U.S. Mint. Please post new question. Is it a quarter or a silver dollar?
about 134 dollars
Sorry! The US never made solid silver coins.
U.S. half dollars aren't solid silver. They're 90% silver with 10% copper, currently worth about $10.
Sorry! The US mint never made solid silver coins. It would be too hard.
from 500 dollars to 100 dollars depending if its p mint mark
It's not solid silver. U.S. silver coins have at least 10% copper in them. See the Related Question for more information.
any quarter prior to 1961 is currently worth at least 2 dollars in silver content
It is unlikely that you have a clad 1964 quarter, all quarters dated 1964 should be 90% silver, not the copper-nickel clad of 1965-present. Look on the rim of your coin, if it is a solid color (usually solid white but silver tones easily to different colors) it is silver, if it has a line of copper through it it is clad (compare it with a quarter from your pocket change). If it is clad, it is an error and worth quite a bit of money. If it is silver it is worth about $6 for the silver content.
They are worth 4-16 dollars in circulated condition. These coins contain 80% silver!
The US never made solid silver quarters. They would not be hard enough to stand excessive ware during circulation. They were made with a combination of 90% silver and 10% copper.