Below is the interface used by the BasePrice callback.

/// <summary>
    /// Cart Price Request by Batch Object
    /// </summary>
    public interface IBatchPriceRequest : ICartBaseRequest
    {
        /// <summary>
        /// Unique batch ID
        /// </summary>
        public string BatchId { get; }

        /// <summary>
        /// Batch name
        /// </summary>
        public string Name { get; }

        /// <summary>
        /// List of lines present in this batch to be priced
        /// </summary>
        public List<IProductLineItemModel> GetLineItems();

        /// <summary>
        /// List of related lines or parent bundle lines present in this batch to be priced
        /// </summary>
        public List<IProductLineItemModel> GetReferenceLines();

        /// <summary>
        /// Cart context.
        /// </summary>
        public ICartContext GetCartContext();

        /// <summary>
        /// Set error details for all lines in this batch. This also updates pricing status to error
        /// </summary>
        /// <param name="errorDetails"></param>
        public void SetErrorDetails(string errorDetails, string lineItemId = null);

        /// <summary>
        /// Set error details for all lines in this batch. This also updates pricing status to error
        /// </summary>
        /// <param name="ex"></param>
        public void SetErrorDetails(Exception ex, string lineItemId = null);

        /// <summary>
        /// List  the product lines that have thrown no errors so far during processing.
        /// Errors could be due to validation checks, invalid data setup or failure of dependent systems as well
        /// </summary>
        /// <returns></returns>
        public IEnumerable<IProductLineItemModel> GetValidProductLineItems();

        /// <summary>
        /// Gets the product line object using line number.
        /// Option Line can use it to get RootBundleLine LineItemModel.
        /// </summary>
        /// <param name="lineNumber">Line number</param>
        /// <returns></returns>
        public IProductLineItemModel GetRootParentBundleLine(int lineNumber);

        /// <summary>
        /// Gets the product line object using parent bundler number.
        /// Option Line can use it to get ParentBundleLine LineItemModel.
        /// </summary>
        /// <param name="parentBundleNumber">Parent bundle number</param>
        /// <returns></returns>
        public IProductLineItemModel GetParentBundleLine(int parentBundleNumber);

        /// <summary>
        /// Get Realted Line Items
        /// </summary>
        /// <returns></returns>
        public IEnumerable<ILineItemModel> GetRelatedLineItems();

    }