I represent a company that sells musical instruments and accompanying accessories. We have a rather interesting method for shipping on complete instruments. If we ship an instrument to a customer internationally (outside the US) we use FedEx's GreatRates service, which gives a fluctuating price scheme depending on when the product is shipping, available space, and destination. So because this is so tricky and unpredictable, we've decided for international orders only we are going to collect a $100 shipping "deposit" up front from international customers. If the cost to ship is less than that, we'll refund them the difference. If the cost is more, we contact them and charge them what remains. Shipping on these instruments is free to the continental US.
The tricky part is programming this into our cart. I have products in two categories to which this shipping pricing scheme would apply. Essentially my question is how would I program the cart to charge an additional $100 flat rate to customers who buy products from these categories and choose to ship internationally, as well as to Alaska and Hawaii?
Thanks in advance for everyone's help!