Web series: 'deferred pay' = never getting paid

Took a web series gig that offered 'deferred compensation — $500/day when the project sells.' The project was actually well-produced and the director was talented. But it's been 8 months and obviously nothing has sold. I knew the odds going in but still feel dumb. The conditions were fine — 10 hour days, meals provided, safety was good. But working for free is still working for free no matter how nice the set is.