I think one of the cheepest, easiest, and if anything convient ways is the bite back your fears and get on the metro. I know it might seem daunting to some people to get onto a often crowed metrocar with a bunch of french people. trust me i thought i was going to make my self look like a total idiot on the metro being american and all but it was suprisingly pleaseant, but make sure to keep you purse and wallets close which you should do on any subway. but, the french metros are relatavily clean and comfortable.

My wife and I visited Paris in September and had a wonderful time. With the exception of a cab from and to the airport we relied totally on the metro in Paris. It was easy to travel around Paris and a number of the metro stations are a work of art themselves. The French were warm and helpful and we did not find any of the "nasty French" attitude we often heard of in the US. We found that a few basic words of French went a long way when greeting or asking questions.