Ok I'll try to suggest a 'design'
User inputs (things you will type into excel)
* Weight of parcel being shipped
* Destination (Post Code?)
* Desired Delivery Time (next day, 3days, 7days, etc) [optional]
Excel 'knowledge' (things excel needs to know to solve the problem)
* Does the company have different rates for varying weights?
* If so, what are the boundaries (eg, 0-20kg, 20kg-100kg, 100+kg)?
* Also, what is the price/kg for each of these boundary groups?
* Does the comapany change the rate depending on Destination?
* If so, what is the 'formula'? (eg, do they charge £x.xx for the first 50miles, and £y.yy for the next 100miles? - or do they charge £a.aa to deliver to a certain Post Code, and £b.bb to deliver to another? If so, do you know what each of these values is for any possible Post Code you may want to ship to?)
* How do their charges change depending on 'Desired Deliver Time'? (eg, do they add £x.xx on for AM delivery, or do they charge a percentage of the total cost of the item?, what about for the other shipping options (nextday, 3days, etc)?
Output (what excel calculates for you, from the above information)
* The price of shipping the item with each company
* The cheapest company to use
As you can see, Excel can only arrive at the right Output if it has been given the 'knowledge' for any possible inputs. This knowledge that it needs can be quite detailed. But if you know all the answers to the questions I listed, then it is easy to make a spreadsheet that will do what you want.
As I said in my first post, the only thing that makes this complicated, is trying to provide excel with all the 'knowledge' it needs. It needs to know exactly how each company breaks down its shipping prices.
Sorry I can't offer a proper detailed description, but it really does require some more detailed knowledge of how each company break down their pricing scheme.