I concur that it was implied that MC would have won if he paid less than fifty bucks, but therein lies the rub: he has to have actually paid that amount, not used a comp.

Since you opt to consider implied terms, I submit the challenge as framed in Redietz's quote above certainly implied that using a comp to get the room would not meet the challenge.

Really, the challenge got side tracked down the rabbit hole; the question was would the casino ever give the room to anybody, including MC, for fifty bucks (or less)?

Like him or not, Redietz certainly should have known that MC could get a room via comp: the challenge impled no comp would be used.