Generally, used optics do not bring much money and are not usually sold separate from a weapon. you might try eBay or the auction sites. I wouldn't give more than 75 USD for one.
40.00
100-400 or so
$450
50-350 USD or so
5-80 usd
100-400 USD or so
$300-500, depending on exact model and condition.
Bushnell (Banner, Dawn to Dusk) has a 4x12x40 that is a good value. The Best? A matter of opinion I guess. Leopold, Zeiss..
250-500 usd
The marlin model 336 in .35 cal will sell in the range of 200-350 dollars,depending on overall condition and a good bore.The price of the scope depends on the type of Bushnell you have and condition.
There are several different models and magnifications. This is an entry level scope, and is in the $20-$50 range.
model 1500, smith and wesson, 30-06, bushnell scope