Original: Even when the first Chocolate House (an establishment similar to a modern coffee shop) opened in 1657, chocolate was still very expensive, costing 50 to 75 pence (approximately 10-15 shillings) a pound.
Simplified: Even when the first Chocolate house (a store like a coffee shop now) opened in 1657, the drink still cost a lot. A pound cost 50 to 75 pence (between 50 and 75 USD now).