The cost of admission for the Louvre is 11 Euros, in advance you can download the Louvre audio guide from the App store for $2.99 and it gives you a tour and description of all the most see artworks.
Or you can rent the audio guide at the museum for 5 Euros, this audio guide works with a Nintendo DS and it gives you nice images of the art work you are seeing. If you are planing to be in Paris for a few days the Museum Pass is the way to go , as you can purchase it for 2, 4 or 6 days and it provides admission to other museums in the areas as well as "skip the line" entrance.