Paris is an expensive city - no bones about it. A coffee costs 2 euro for an expresso, rising to an exorbitant 4 euro average for a "caffe creme" - with steamed milk. Food also tends to be on the high-end side. But there's one way to really save money in Paris - and that's its extraordinary and functional public transportation system. The metro is a great option to quickly get where you need to go; the spiderlike shape of its map is highly convenient in that it reduces the needs for line changes. But there's one new option that's even better: the Velib.
The Velib (Velo Liberte) is a system of bikes that has taken Paris by storm. Stops, each with places for 20 or so bikes, are located every few hundred metres around the city. You rent bikes from one station, ride them, and deposit them at any other with free spaces available. Even better? A one euro day pass gets you the first half hour of any ride free, and reasonable (though steadily climbing; don't get the whole bike for one day) rates after that, although if you wait 15 minutes after depositing the last one, the clock starts back at 0. And if you come to a station and it's full? No worries, just type in your login code and you'll get 15 minutes grace time and directions to the next available posts.
If you have a chipped credit card, you can buy passes (1 euro for a one-day, 5 for a weeklong, and the option of yearlong credit on your Navigo pass for residents) at the kiosks themselves. If not, you'll need to go to a Tabac and purchase it there.
Seeing the city, getting exercise, and participating in a ritual that's captivated a whole generation of Paris commuters - the Velib isn't just a method of transportation, but an adventurous highlight of your trip!