Flat Shipping Based On Number Of Products By Category

I am struggling to figure this out.

Currently the store I am running sells equipment and music. The equipment shipping is calculated based off weight and dimensions in real-time.

There is a free shipping promotion if you order more than $100.

Where I am struggling is …

I have a set of categories that sell music. I need to setup shipping to be flat rate for these products based on the number of items purchased in these categories.

For example,when ordering from a particular set of categories…


[] If you order 1 item, shipping is $2.00.

] If you order 2-4 items, shipping is $3.00.

[*] If you order 5+ items, shipping is $5.00.


I have been racking my brain with the promotions and shipping charges, but I cannot come up with the scheme to make it work. Any suggestions, modifications and general advice would be more than welcomed.