Whatever they want for them!!! Seriously, they are worth it. Being that large though, I'd expect to pay $100 plus each. Especially since they are 'green's. But who knows, maybe someone will sell them for less, much less.
His was a little bigger, around 15 to 16". . . . It all really depends how fast your friend wants to move them. Put a higher price on them, they will probably move slower. JMO.