How to setup a product with no price

[bengalliboy]

Hi

I will need to setup a product which does not have any price. Let me explain. This product will have a weight and I know the price per lb is say $2. However when users buy it I can only tell the range that is the product may go between 10 to 15 lb. So I can't say that it is actually 10/11/12/13/14/15 lb.

 

After users place the order then I process it and get the actual weight.  Since it is COD (Cash on delivery) I want to adjust or tell the user at the time of pick up or delivery that is exactly 12 lb so the price is 12 * 2 = $24 

 

So how do  set this up? Do I need a reservation module or can I simply do this with a way so that it does what I want.  Please help. Thanks!