How many hours should a single player game today be to warrant a sixty dollar purchase?

[Cirio]

I value my purchases based on a simple ratio, 1 hour = 1 dollar. If I see that I won't be playing the game (sp and mp combined) for at least 60 hours, then I don't buy the game for $60. So for a single player only game, if I were to buy it for 60 dollars, then it better give me 60 hours minimum of play time (multiple playthroughs count too, like for Mass Effect 2).