Is this possible....

[digilexic]

I have different categories, like small, medium, large

 

I want to charge shipping by category (every item in the category has same shipping rate) like so

1st item is large green widget, it costs 18.00 to ship each additional large widget from the same category is 8.00 to ship

2nd item is medium blue widget, it costs 8.50 to ship, each additional medium widget from the same category is 3.00 to ship

 

I need to be able to charge the full shipping on the most expensive shipping option, and then the additional rate for all the others...

 

So say a customer orders a large widget category item and a medium widget category item, they would be charged 18.00 for the large widget, and 3.00 for the medium widget

 

I cant seem to find any modules to do this. Perhaps someone can point me in the right direction.