How to use gravity form as a cost estimator?

I am working on a logistic website and I want to use gravity form as a cost estimator.

Here is a scenerio, I have different shipping prices for different regions for my form.

Example New York to New York (Delivery charges is $20), New York to New Jersey ($30) and so on.

The user will select their resident state from a dropdown and select the delivery address from another dropdown, how to i assign delivery cost to dropdown value as they are selected.

Thanks

via Chebli Mohamed