I would like to adapt zen car shipping module to handle the following logic. Each item has a shipping cost - to calculate the total shipping cost apply the following algorithm
If the shipping price is under $[url removed, login to view] then...
The 1st product will have 100% shipping.
The 2nd product will have 50% shipping.
The 3rd product will have 25% shipping.
Anything under that will have 20% shipping.
If the shipping price is over $12 then apply no discount use the whole shipping amount.
Please make sure these percentages and amounts can be changed.