IIRC the last time this was sold publicly was in a Neiman Marcus Christmas catalog a few years ago and the price was $3m (I think I remember $5m for a companion version as well).

As for why Cuban would buy these for his folks when he already owns planes; private planes are expensive to operate and I'm certain he wouldn't have paid retail for the passes he bought. Remember, in addition to owning aircraft, Cuban owns the Dallas Mavericks, and where do the Dallas Mavericks play their again?!?!