I don't think you can use bread as any kind of indication. In the 14th Cent. bread was all handmade by bakers, who obviously had to be able to charge enough so that they could support their families, buy their yeast, weat and fuel for the ovens etc. In 2006 bread is made in huge factories and distributed to huge supermarkets in huge lorries, so the price of bread, which is just a few pence for a cheap loaf must be lower in real terms that it was in the 14th century.