Per Unit Weight for two different zones

We use a courier that charges two different rates depending on the area of delivery. They have a list of Major Centres (12 large cities) in our country and the other areas are Regional Centres.

They have a rate based on weight if delivered to Major Centres, lets say for every 1lbs it costs $3. Now if you require a delivery to other regional areas, they charge the normal $3 per 1lbs + an additional surcharge of $2 per 1lbs.

I have my two zones setup already, but cannot seem to find a shipping module that would do what I want to do. Would I have to custom make this? or can someone shove me in the right direction to get this working.

Perhaps this thread will help? http://www.zen-cart.com/forum/showthread.php?t=101754

Thanks Kim, I had been working with the cloned table rates, having to input every weight individually, which was cumbersome, was wondering if there was a mod that worked, from here to here = price per unit, iow: up to 10kg would be 2.5 per kg, would equal 250 total. Maybe I can mod the table rate....

Thanks