You can probably get about 95% of the value of the silver in the rounds and bars if they are marked .999 fine. Dealer will use the spot silver price which is about $45.50 today. Note that silver trades in Troy Ounces, not the ounces you see on your postage scale.

Your pre-1965 silver coins should sell for about 95% of the bag price, which is just under 33 times face value of the coins.

The 40% silver halves are less in demand, but probably worth about 13 times face value.

As with all coin sales, the price offered to you will depend on the dealer you use and how much he wants more coins to inventory. Small quantities will always bring you less money than bag quantities ($1000 face).

Bullion coins sell on eBay every day so you can always sell them that way. You will find that no one will bid on them till the last day of the auction because they want to get them near the value of silver on the day they buy the lot. Remember you will pay about 9% in sales commissions when you sell on eBay.