Which term refers to a substantial cost associated with products or services?

The phrase "will cost you an arm and a leg" is an idiomatic expression used to describe something that is very expensive. It effectively conveys the idea of a substantial financial burden associated with purchasing a product or service. This expression emphasizes the high cost in a metaphorical way, suggesting that the expense is so great that it feels like giving up something very valuable.

The other choices do not relate to costs in the same way. For instance, "green around the gills" refers to someone who looks unwell or nauseous, while "offering of fake cure" implies dishonesty regarding treatments, which does not address the concept of cost. "Strenuous" refers to something that requires a lot of effort or exertion, and also does not pertain to financial matters. Thus, the selected term directly connects to the idea of high costs, making it the most suitable choice.