What's the value of non-cashable free play?

I've received numerous offers for slot tournaments where the prize is a combination of cash and free play. What's the value of the free play? I think the easy answer is face value of the free play times the slot return percentage but I don't know if that's completely accurate. If you were given $10,000 in free play as a prize should you be issued a 1099 MISC tax form on it? What if you played the free play and won nothing? If I had an option of $10,000 in free play with no taxes or $10,000 in cash with taxes I'd take the free play, assuming I planned on coining-in at least that amount on the slots. Anyone ever had this happen to them?

Mark