Hello,
For your transportation in Paris and Paris suburbs, the cheapest and most comfortable is Paris Taxi Cab.
You can order for a simple transfer or special tourist packages for half day, full day, 2 to 5 days at very competitive prices.
For a 3 days tourist package for example, it will cost you only 70 euros per day for 80 km and 8 hours in a very comfortable vehicle and a driver at your disposal.
You can check the prices directly on the blog http://paristaxicab.over-blog.com