Extended View model

 public class ProductPriceFieldAttribute : FieldAttributeBase
    {
        public override IEnumerable GetFieldValues(IField field, IModelProperty property, ITemplate template, IViewModelFactory factory)
        {
            IEnumerable fieldValue = null;
            var productId = field.Values.FirstOrDefault();

            var productService = new ProductService();
            var price = productService.GetProduct(productId).Price;
            
            return new[] { price };
        }

        public override Type ExpectedReturnType
        {
            get
            {
                return typeof(double);
            }
        }
    }