You don't need to fly Air France in order to use "les Cars Air France" (the Air France buses).
Quite right. We always take the AF shuttle from CDG to the Gare de Lyon.
I think there are 4 lines, but they go to stations (and Roissy), not hotels. I think the price is reasonable compared to the RER/Metro option since the AF shuttles are much more convenient.
http://http://www.airfrance.com/doub...F?OpenDocument
If one wants transport direct to a hotel, it's best to reserve one of the private shuttle services. I'll try to remember which one our usual (small) Paris hotel uses; they're pretty efficient, and, while not cheap, they're still a lot cheaper than a taxi. That's a total ripoff.