If you book your son's ticket NOW at www.tgv-europe.com, he can get a Prem's fare of 22 EUR on the TGV leaving Bordeaux at 16:43 and arriving at CDG at 21:12 on 5 January. The site says, "Hurry, last seats available!" so you'll have to act fast to get this discount fare. To keep the site in English and to keep from being bumped to the Rail Europe site which doesn't offer discount fares, choose Great Britain as your country of residence. After you book the ticket, you print it yourself.
The Accor chain has several hotels in a wide range of prices close to CDG. The cheapest is the Formule 1 Roissy Aeroport CDG PN2. Shared bathrooms are down the hall. The next cheapest is the Etap Hotel Roissy CDG Paris Nord 2. Bathrooms are ensuite (in the room). Both hotels offer free shuttle bus service to the airport.
If your son and his friend decide soon what day they will travel from Paris to Bordeaux and act quickly, they probably can get Prem's fares for that trip, too. One of them should book both tickets so they get adjoining seats.