Nishikori’s Wimbledon Air Zoom Vapour X

By some means or another my cousin has ended up with Nishikori’s Air Zoom Vapour Xs from Wimbledon this year and I was wondering if anyone could suggest how much they are worth and what the best way would be to go about selling them. Thanks in advance.

I’m having trouble attaching an image of the shoes but they are visible in the image at the top of this page...

Nishikori’s Wimbledon Air Zoom Vapour X