Rails select form: displaying and using select form value before submit?

I am working on a multi step form for an order placement process. In it I have two selectors for shipping countries and shipping services. After selecting the country all shipping services are displayed for a given place and weight. When the order is placed everything is written to the model. All the shipping details process is done through a multistep form following Ryan Bates #217 Multistep Forms

The shipping service selector is populated through a javascript ajax call after the shipping country has been chosen. I followed this two tutorials Dynamic select boxes with Rails 4 and Dependent country city state.

$(document).on("change", "#lands_select", function(event){
  $.ajax({
    url: "/carts/update_shipping/" + event.target.value,
    type: "GET"
  })
});

update_shipping.js.erb

$("#shippingservices_select").empty()
  .append("<%= escape_javascript(render(:partial => @shippingservices)) %>");

_shippingservice.html.erb

<option value="<%= shippingservice.id %>"><%= shippingservice.name.titleize %></option>

In addition to this I would like to display the shipping cost related to the selection made in both selectors below the form together with the calculated total shipping cost.

How can I do this? Since both values have not been written to the order database yet I would have to display the resulting price of the second selector selection which is inside the shipping services table, but since the order has bot been written yet I cannot call it through the order instance variable. My guess is that I would have to do this adapting the ajax call, could that be? How would I have to do this?

What I have now is that the form is populated through json produced by the order controller's update_shipping action as far as I understand.

Thanks in advance!