Our company provides several delivery methods, some of which are:

· Free Delivery to "CityX" (Carrier: Self)

· (Free if > $ 1000) Delivery to "CityY" (Carrier: External)

(Actually, the second option delivers to more than 1 city)

If we get a sales order from a customer that doesn't resides in either of the cities we deliver, we offer to deliver the goods to another carrier, chosen and paid by the customer. (**the carrier needs to have a dropoff site in either of the cities we deliver)

So, our possible shipments go like these:

Our company -> Self Transport to "CityX" -> Customer Delivery Address

Our company -> Self Transport to "CityX" -> Another Carrier -> Customer Delivery Address

Our company -> External Carrier to "CityY" -> Customer Delivery Address

We are wondering what would be the correct approach and if there's any module out there that already handles this case. (it's actually very common in our country, where high load carrier companies don't handle deliveries country-wide)

If not, what would you suggest?