Shipping for numbers of items (1-20=$50, 21-40=$100, etc.)

[Peat]

Hello!

 

Is it possible to have a shipping cost set by number of items (in a category)?

 

Example: 

 

We only use on shipping vendor USPS, and we can fit up to 20 items into one box.

 

We want a flat Shipping and Handling fee for every 20 items sold that are in one category.

 

All other categories will have their own directly related shipping and handling costs.  

 

Examples:

 

1-20 items, flat S&H of $50. 

21-40 items flat S&H of $100.

41-60 items flat S&H of $150 etc.

 

I hope that makes sense.  We are using Prestashop 1.6.1.6

 

Thanks!

 

Peat