The correct answer is 'Discounted pricing as service usage increases.' AWS employs a usage-based pricing model, where services may come with tiered pricing. This means that as a company utilizes more of a given service, the cost per unit can decrease, which is a direct benefit of economies of scale. The company pays less per unit as it consumes more, leading to cost savings. The other options provided are related to general cloud benefits but do not directly address economies of scale. 'Fixed monthly subscription regardless of usage' is incorrect as it implies a flat fee model not associated with variable usage. 'Uniform global pricing for services' is also incorrect since it refers to consistent pricing across regions rather than cost reduction from increased usage. 'One-time upfront investment in infrastructure' is incorrect because it describes a capital expenditure model typical of on-premises environments, which contrasts with the cloud's variable expense model.