Yes the Queensboro Bridge is walkable and has a walking and cycling path on the Queensboro Bridge and it's a narrow path along the northern edge of the bridge.
It can get pretty crowded though but you can walk or bicycle along that path on the Queensboro Bridge.
The Queensboro Bridge is a long five-span, two level cantilever bridge that connects Midtown Manhattan and Long Island City in Queens NY.
The Queensboro Bridge spans the East River and Roosevelt Island of NY, which used to house a number of public institutions, including a prison.
There's no toll to cross the Queensboro Bridge.
The Queensboro Bridge is operated by NYC DOT and any bridges or roads operated by NYC DOT require no tolls to cross them.
So you can cross the Queensboro Bridge with no toll.
NYC DOT owns, operates, and maintains 789 bridges and tunnels throughout New York, including the Brooklyn, Ed Koch Queensboro, Manhattan and Williamsburg Bridges, 24 movable bridges, and four tunnels.
There are no tolls on bridges operated by NYC DOT.
So you can cross the Queensboro Bridge or any of those NYC DOT owned and operated bridges as many times as you want too or need too without paying a toll to cross them.