A more effieint method of getting around Paris than walking,and a cheaper way than a taxi…the Paris Metro. Paris is divided into five zones, but I could not see any reason why you would want to go any futher than zones 1-2. You can learn from here what tickets to get before you even land into the city.
Mobilis is a pass for one calendar day. The price depends on the zones where you intend to travel; if you plan to stay within the city, a zone 1 pass is all you need.
The basic Metro ticket costs €1.90, but a cheaper way to go is to buy a carnet of 10 tickets for €14.50 in the station itself. A single ticket will take you anywhere within the city of Paris on the Metro and RER networks, and you can transfer between lines or between the Metro and the RER on the same ticket.
You can also use T+ tickets on buses and trams, although you can’t transfer between the Métro and RER and buses or trams on the same ticket.
Metro tickets for Under 25 year olds can get an unlimited (zone 1-3) weekend ticket for €3.75!
I would still recommend walking until you physically can’t anymore before you give into the metro system. Paris has so many charming streets it would be a real shame to spend your time smuggled underground.