Opening Mega Evolution Elite Trainer Box [Mega Gardevoir] returns about $33.07 in card value against its $122.47 price — roughly $0.27 back per dollar spent. On current prices, you lose money on average by opening it.
See every card and pull rate in Mega Evolution
How expected value is calculated — card value only, from published pull rates and daily market prices.
Mega Evolution Elite Trainer Box [Mega Gardevoir] on TCGplayer