Taxi prices vary - there doesn't seem to be a definite price. I've heard all sorts - from 40 to 100 euros!!! You can always take a chance when you get to CDG or, if you want to know what to budget for, you could prebook with a shuttle company as Liz did. RS Transport seem to be a reliable and fairly reasonably priced option.
When you land after picking up the luggage, there will be a bunch of guys standing by the doors proclaiming they are taxis... do not take those. Go to the official taxi station, I believe it is door 20... but just follow the sign. It will cost you around 100+ euros from CDG.