yeah, but Paris transport is very expensive.
Are you sure? Well of course it's an investment but it can be very useful and not that expansive if you use it a lot.
Like you can buy a "carte orange" for one month at about 15 euros, usable in both the métro (and the the RER) and the buses in Paris and the close suburbs.
Or there is a transport pass specially designed for tourists usable during 1 to 5 days etc... in all means of transport except the taxis i think so the métro, the RER (regional train), the buses (night and day) and the boats etc... Lots of tourists use that.
Have you checked this website? http://www.ratp.com/
Good luck with your preparation of your trip!