A Penny For Your Thoughts — Robert Ford

Fresh from a stretch in prison, Joe Openshaw is living at home with his father and trying to get his life together again. He has let go of old habits, especially the ones that turned him into an addict and helped land him in prison.
On a hike along the Lowback Trail, Joe stumbles on one of the town's oldest secrets--buried long ago, if not forgotten.
It's an unusual but safe enough treasure--a jar of old pennies. What interests Joe isn't the pennies themselves, but the pieces of paper taped to every coin--a child's handwritten wish on each one.
When the first few wishes come true, they are simple things. Fun. Harmless.
Except as time goes on, Joe realizes they aren't really wishes at all...they're exchanges, and the bill was racking up.
Nothing is free in life.
Sooner or later, you always pay.