Hi,
You can use the Shipping Zones Module. More information how to set them up in this tutorial...
https://www.zen-cart.com/tutorials/index.php?article=69
Example how i set them up for a client..
Zone 1 Countries
UK
Zone 1 Shipping Table
5:5.00,9:7.50,13:10.00,17:12.50,21:15.00,25:17.50,29:20.00,33:22.50
Zone 1 Handling Fee
0
Zone 2 Countries
AT,BE,HR,CY,CZ,DK,FI,FR,DE,GR,HU,IE,IL,IT,LV,LU,NL,NO,PL,PT,SK,ES,SE,TN,TR,
Zone 2 Shipping Table
5:10.00,9:15.00,13:20.00,17:25.00,21:30.00,25:35.00,29:40.00,33:45.00
Zone 2 Handling Fee
0
Zone 3 Countries
US,CA,AU,NZ,
Zone 3 Shipping Table
5:15.00,9:22.50,13:30.00,17:37.50,21:45.00,25:52.50,29:60.00,33:67.50
Zone 3 Handling Fee
0
This was using the zones based on weight and having all products set to the same weight of 5lbs to give the following set of rules...
UK
1st item £5 each item thereafter at £2.50
Europe
1st item £10 each after £5
Rest of world
1st item £15 each after £7.50
All that is also based on flat rate shipping.
Hope this helps you on your way to resolving your issue.
Rob