However, I am having a little trouble with my custom shipping logic.
At the moment I'm using this formula:
$shipping_price = 4.00 + (($total_quantity - 1) * 1.50);
In that it is $4.00 for the first $1.50 for each item after that. This works perfectly, however I do want to add something. I was wondering if there was a way to make this not apply to all the products. Or even better, make it so when certain products are added, an amount is added, like an amount in a user field or even the shipping cost field is added. Because the items in my store range from large to small, so do the postage amounts.
I hail from Australia so all the UPS and FedEx stuff doesn't apply, if that helps

I'll eloborate more if needed. Any help would be stupendously appreciated.