Cost-effective cloud storage services attract users with their convenience; there is a trade-off between the service availability and the usage cost. We develop two cloud provider selection models for cloud storage services to minimize the total cost of usage. The models select multiple cloud providers with considering unavailability to meet the user requirements. The first model, called a user-copy (UC) model, allows to select multiple cloud providers, where a user itself makes copies of its data for multiple providers. In addition to the user copy function of the UC model, the second model, which is called a user and cloudprovider copy (UCC) model, allows cloud providers to make copies of the data to deliver them to other cloud providers. The cloud service is available if at least one cloud provider is available. We formulate both models as integer linear programming (ILP) problems. Our performance evaluation observes that both models reduce the total cost of usage, compared to the single cloud provider selection. As the cost of bandwidth usage between a user and a cloud provider increases, the UCC model becomes more beneficial than the UC model. We implement the prototype for cloud storage services.