I am betting against expensive oil, so expensive beef would help me win the wager, though if I win due to cattle scarcity that would not very well serve my larger point that material welfare is getting better for people over time.
I'm not sure I would agree that rising meat prices would be antithetical to the idea that material welfare is increasing. Given the myriad externalities that aren't currently priced into meat, rising prices might actually be more reflective of the rising consciousness of a more educated and savvy population. Government regulation has created an artificial price support for meat, and if it were allowed to expire, you would win the bet by 10-fold. Agriculture is a hard one to make a Simonian bet on, given that he tried to (it seems based on my very minimal knowledge of the man) make bets that were freer of government price interference. Oil has some, too, but not anywhere near the level of meat.