One way to cut down on the taxi "approach" charge is to call a nearby taxi stand:
http://www.taxis-paris.fr/telephone-bornes-taxis.htm
This works especially well if you need a taxi NOW and there happens to be one at the stand.
The disadvantages there are that
- there may not currently be any taxis at the stand
- the driver who answers may not speak English
- you can't request a certain type of vehicle (for instance, a mini van if you have a lot of luggage or several people)
Also, be aware that many Parisian taxi drivers won't wait more than a few minutes for you if you're not ready when they arrive.