Configuring own shipping rates

Hello ya'll, I will try n write this as best as possible so you understand what I am asking hehe, I'm getting to grips with zen cart in general but the shipping has SCUPPERED me big time! :dontgetit

Right, i am selling beauty, handbags n jewellery mainly on my site and this means the weight in items are so different. I have incorporated the cost of royal mail postage into the price for our uk customers but need to then add in the difference in price for said item to either europe or worldwide.... One of our pledges is NOT to overcharge customers what so ever, we only wish to charge what royal mail charge however, there are so vast differences in the prices for europe n worldwide, we have worked out a banding system A-H for the additional postage fee to add on top of the price, ie cost of foundation for uk is xx amount including postage, but the customer lives in europe and therefore would incur extra xx amount to post to them,, when it comes to checking out, we want to have the option to click Option A for example as this is the price difference for that item but i cant fathom how i would do this.

I do hope im making sense with this.. the customer will not know the weights or anything it is simply for our benefit that we know whether an item will be band A or band h and we will note this on the product listing as BAND A BAND C or what ever, erm,, i mean if anyone has a better system in place for this i would also be very open to other suggestions??

(I am using zen cart version 1.3.8

Sincere regards

Claire Riding