Go into the Anno 1503 Folder and open  the DATA Folder. 
There you find the file: "BGruppen.dat."

Open this file with any text editor.
Look now in the file after the section for the consumer goods.

Now you can change the prices for these goods freely as desired. It plays 
thereby no role, how highly you screw the price, your village inhabitants 
it will pay and you to a positive balance will thus help.