You can find here an info how Amazon handles shipping costs
http://www.amazon.com/exec/obidos/tg...f=br_bx_c_1_0/
As we explored they don't use shipping costs based on the price. And they write
"How are shipping costs calculated? We charge a single flat fee for each shipment, plus additional, smaller fees for each item in that shipment. The total shipping charge will be displayed on the last page of the order form, before you submit your order. Here is the equation we use to calculate the total shipping cost:
(Highest Applicable Per-Shipment Cost) + (Number of Items x Per-Item Cost) = Total Shipping Fee
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But most of the shopping carts support the shipping cost structure you plan to use.