Believe you will need to use script or report SQL details report with an sql query something like this;
SELECT p.[Price]
FROM [MenuItemPrices] p
LEFT JOIN [MenuItemPortions] s ON s.[Id] = p.[MenuItemPortionId]
LEFT JOIN [MenuItems] m ON m.[Id] = s.[MenuItemId]
WHERE m.[Barcode]=1234 AND s.[Name]="Normal"
On the presumption your only using normal portions and a single price list.
NOTE this query doesnt work, think it needs tweeking due to the [Name] column being used in multiple tables of the joins.
Obviously you would need to input the scanned barcode as a variable.
EDIT
Actually the issue is posibly due to my multiple price lists.
if you only have one price list and one portion to a product it might work just with barcode WHERE but would not be fool proof.