public interface IProductPrices
    {
        int ProductId { get; set; }
        string ProductCode { get; set; }
        List<IProductPrice> Prices { get; set; }
    }

public interface IProductPrice
    {
        int ProductId { get; set; }
        string PriceKey { get; }
        double Price { get; set; }
        int Id { get; set; }
    }

//productPrices is of type IProductPrices
//temp is of type IProductPrice

........
var finalPriceList = new List<ABC.Model.ProductPrice>();
foreach (var item in productPrices)
    {
        foreach (var temp in item.Prices)
        {
            var prodPrice = new ABC.Model.ProductPrice()
            {
                Price = temp.Price,
                ProductCode = temp.ProductCode
            };
            finalPriceList.Add(prodPrice);
        }
    }
.....

foreach (var temp in item.Prices)