As hard as it will be, I agree that its best for the turtle to be in the wild.
I'm unsure if it's illegal, though. Here in Arkansas they don't say its illegal, but I know for certain its that way in Missouri (I live close to the Arkansas-Missouri line... and i know you don't live in Missouri, Lute.).
Petstore turtles do have quite a pricetag (box turtles here at Petco are around $70-some), but at least he would be domesticated.
Good luck on whatever you decision may be.