See, this has been bugging me! :\
Here's the quote from the
SRD re the Craft skill which defines the cost of raw materials:
To determine how much time and money it takes to make an item, follow these steps.
1. Find the item’s price. Put the price in silver pieces (1 gp = 10 sp).
2. Find the DC from the table below.
3. Pay one-third of the item’s price for the cost of raw materials.
4. Make an appropriate Craft check representing one week’s work.
That's why it costs 1/3 of the market price. Bront's comment to me was to advise that this has - at some point - been adopted in LEW.