There is an Ibis hotel right at CDG. It's close enough that you can easily get to the free CDGVAL driverless shuttle train which operates 24/7 between all three terminals and the CDG 1 RER station. See here: http://tinyurl.com/2nylg8.
If you decide to stay in Paris, your cheapest option would be to take a taxi to Chatelet and a night bus from there to CDG. Noctilien #120 leaves Chatelet at 03:30, arriving at T2 at 04:10, T1 at 04:15, and T3 at 04:20. The next #120 bus leaves at 04:30, etc. Noctilien #121 leaves Chatelet at 04:25, arriving at T2 at 05:05, T1 at 05:10, and T3 at 05:15. The fare is four single tickets (a total of 6€).