The correct answer is D. Pay-as-you-go pricing. This pricing model allows companies to pay only for the cloud resources they actually use, without the need to estimate infrastructure capacity in advance. This aligns with the company's requirements to eliminate guessing infrastructure needs and to spend budget only on resources as they are consumed. While economies of scale (option C) do contribute to lower costs in the cloud, it is the pay-as-you-go pricing that directly addresses the company's specific needs mentioned in the question.