score:3
in fact, navigo is just the new carte orange.
so for the price, so you have, with the navigo card, three different time length for navigo:
week (for zone 1-2, (paris only), 19,8€) from monday to sunday
month (for zone 1-2, (paris only), 65,1€)
year (for zone 1-2, (paris only), 679€)
Note that a Navigo monthly or yearly pass (but not a weekly pass) is valid for the whole Île-de-France region on week-ends and public holidays.
the difference beetween navigo and navigo decouverte is navigo vanilla is personal and you have to go to an ratp office because they took a photo of directly in the chip card. fro vanilla navigo, there are only one part.the vanilla is only for Parisian people.
the navigo decouverte is the two part card more like the old carte orange. easier to get, you can have it without to go to ratp.there are two part. a chip card without identity and and a card where you write your name and put a photo. you need to have cards to travel but it's the chip car the card who need to be recharged.
i think you buy a card for you friend and put photo after.
about the choice for zone, as i said before, the smallest subscription is zone 1 and 2 but the zone 3 is quite near( for exemple you have la defense in zone 3) you can see all the maps in english there http://www.ratp.fr/plan-interactif/carteidf.php?lang=uk but if you take a small zone, you can buy a "complement de parcours" and go outside.
NEVERTHELESS there are other subscriptions as paris visite, for exemple.