Shipping with Flat Rate USPS, Extension for sale?

Hi Friends,

I need a solution for my website at helircstore.com

Situation: using OpenCart 1.5, I need to find if there is a extension we can purchase to do the following--

We ship many small parts---customer adds product to cart, part is 8 oz, then customer adds another of same part, and shipping jumps up beyond USPS First Class Mail Postage as it should, all is good idf they just order 1 part, how do we integrate small flat rate Boxes for USPS so customer only has to pay the going flat rate price for that small or medium box? Since many small parts can fit in those containers, saving customer money is important to stay competitive !


I enabled small flat rate box under shipping for USPS, I do see priority shipping however not the flat rate price of 5.20 ?

So the bottom line, how to integrate small or medium flat rate USPS rates for our parts only?

We are willing to purchase a solution!

Thanks,
B-