It is almost always only one side of coin and usually the coin displays some weaker striking characteristics due to the planchet being thinner than normal.
Values depend on the condition of the coin and the grade assigned by a grading company. It can also depend on the date and mint of the coin since some coins are low mintage key dates. The values listed below sample known final values of sold coins and then that is averaged, so I listed a start and a possible high, but often this had to be estimated based on the research.
Partial cladding missing will trade at a reduced rate and double sided would increase.
Roosevelt Dime: $45-$130
Washington Quarter: $84-$105
Satin Finish Quarter: $400+
Kennedy Half Dollar: $250-$300
Eisenhower Dollar: $450-$1,000
Susan B. Anthony Dollar: $150
Sacagawea Dollar: $500-$920
Presidential Dollar: $260 and up
Also see Plating Issues
Image courtesy of Heritage Auctions