Sue, Paris is a much larger city than Barcelona and the hotels are really spread all over the place. It is going to be a bit difficult to find a decent place for $120, but it probably does exist somewhere (I do not know where). You certainly should do some research at tripadvisor.com as they have a lot of hotel info and a decent forum. We have a place we like a lot that is located in a residential area of the Latin Quarter. This hotel has no A/C and madame does not speak any English (although her daughter is fluent) and its within a couple of blocks of the metro and buses. The web site is
and you can draw your own conclusions. Getting to this place (or any hotel) from the airport can be done using the RER and Metro lines. But since this is your first time in Paris you might want to reserve transportation on one of several transfer companies (just use google and you will find a few) that can shuttle you from airport right to your hotel. Make sure you save your pennys before your trip, because you are going to find Paris quite expensive (thank the lousy dollar). This being said, my wife calls this city her favorite city in the world and would say its worth every penny.