Don't forget to consider the price for packaging and advertising. Those four nuts for six dollars come in a plastic bag, propably sealed by hand, with nice color printed cardboard stapled on top. The nuts are advertised in color in no fewer than 3-4 seperate magazines.
Cost distribution for four nuts at 6 dollars all prices are estimated.
Nut manufacturer. $0.15 each, 0.60 each bag.
Plastic bag. $0.20 each bag.
Cardboard, punched and printed. $0.80 each bag.
Staples. $0.001 each bag.
Machines to count, package and seal the plastic bags 100,000.00 each. Lets say they make 1,000,000 bags before the machine dies. Then it's $0.10 each bag.
Manning the machine. $5,00 hour (cheap labor) 500 bags each hour. $0.01 each bag.
The list goes on and on.
Housing for the packaging machine and storage, shelves for storage.
Design for cardboard.
Packaging the bags into boxes for stock.
Removing bags from boxes for shipping.
Hobbyshop/mail order companys cut.
Think about this. It would only cost about half dollar more to have 8 nuts in the bag instead of four, almost all the other costs are independant of quantity.