Comparing prices among the major IaaS cloud vendors is not as easy as simply checking the cost of one virtual machine versus another. There is a wide range of factors that influences price: size of the virtual machine, its type, and contract length, to name a few.
So how are you supposed to know which vendor offers the best deal? In deciding this, it should be kept in mind that the most expensive way to pay for cloud-based virtual machines is on-demand: the longer you plan and commit to using these resources, the more you save.
So for example, with Azure and AWS the way this is done is by using Reserved Instances (RIs), and the more you pay for usage up front, the greater the discount (ranging from 24-75% when compared to on-demand). With Google, their model for incentivizing usage is called Sustained Usage Discounts (SUDs), and again, the more you spend, the more you save.