Question: What is the train route from Charles de Gaulle airport to Calais? I see that there is a train station inside the airport. Is there only one station or many? If there are many stations please let me know the station name and the train to board and the route.

I hope the train is the cheapest and best mode to travel from CDG to Calais, if there is any other please suggest.

Answer: 
You'll need to decide your price / time balance. You can save money by taking the bus but it's slower than by train.

As mentioned you can take the train directly from CDG Terminal 2. Some require a change, or even change between two different stations, in Lille. Details here [Voyages-SNCF](http://www.voyages-sncf.com/). Generally from around €30.

Eurolines does have one direct bus most days from the airport directly to Calais. You can save even more though by going into Paris and catching a bus from there. You can compare bus options [here on Busbud](https://www.busbud.com/en/bus-paris-calais/r/u09tvm-u113f5) (full disclosure: I work on this project). Generally from around €10.
The train station is located in Terminal 2 (between 2D and 2F).

Not sure if the train will be the cheapest way to go to Calais. The bus or a shared car might be cheaper (but also take more time).

For instance, with the bus, you can get to Lille from CDG for just 9€ :
<http://uk.ouibus.com>

Then from Lille to Calais, with the bus, train or shared car, it will be less than 30 €.

For the shared car, try this :
<https://www.blablacar.fr/>

Hope this helps! :)