public interface IRepositoryFactory
    {
        IProjectRepository CreateProjectRepository();
        IConfigurationRepository CreateConfigurationRepository();
        ICostCategoryRepository CreateCostCategoryRepository();
        ICostRepository CreateCostRepository();
    }

    public class SampleRepositoryFactory : IRepositoryFactory
    {
        private IProjectRepository _cachedProjectRepository;
        private ICostRepository _cachedCostRepository;

        ...


        public IProjectRepository CreateProjectRepository()
        {
            if(_cachedProjectRepository == null)
                _cachedProjectRepository = new SampleProjectRepository();

            return _cachedProjectRepository;
        }

        public IConfigurationRepository CreateConfigurationRepository()
        {
            ....
        }

        public ICostCategoryRepository CreateCostCategoryRepository()
        {
           ....
        }

        public ICostRepository CreateCostRepository()
        {
            ...
        }
    }