Cloud computing is an on-demand network access model to a shared pool of configurable computing resources. One of the main challenges in cloud computing is the efficiency of the pricing and resource allocation models adopted by cloud providers. In this paper, we proposed a new resource allocation model called ARAM, which is based on reverse auctions and provides dynamic pricing policies. In this model, independent reverse auctions are hold for each cloud service request. ARAM has been compared with other previously proposed approaches, considering several issues such as the types of the services it supports, the necessity for configuring service instances, and also those related to load balancing. The main advantage of ARAM, compared to previous forward auction based models, is that it eliminates the necessity for configuring service instances. Therefore, the utilities of both consumers and providers are enhanced, in terms of cost and time. Also by adopting a dynamic pricing approach, it moderates the shortcomings of fixed pricing strategies in cloud computing, such as resource wastage and lack of fairness. Furthermore, contrary to most of the previous approaches, ARAM supports dynamic pricing for all types of services and considers load balancing issues in allocating resources. Today, most of the providers in the industry use fixed pricing models ignoring the market condition. Therefore, it seems necessary to use efficient dynamic pricing and resource allocation models, such as ARAM, in cloud computing.