How much do silver coins sell for?

Most old US silver coins were made of 90% silver and 10% copper (*) so at worst you'll get their current metal value from a scrap dealer, minus their profit of course. That varies depending on the current price of silver so you'll have to check a site that monitors prices.

Of course, most of those "we buy old coins" places will take a heavy cut for their profit so you might be lucky to get 1/2 to 2/3 of their raw metal value. Also, depending on the coins' dates and conditions they might be worth a LOT more to a collector so selling them for scrap would be like selling a painting for its canvas. If any of the coins are earlier than the 1950s you should check out their collector values before selling.