Ski passes (abonnements) can be purchased from the cable car at Morillon. 

Either get Secteur Massif which gives access to Morillon, Samoens, Le Carroz, and Sixt or if you get a Grand Massif pass this includes Flaine as well.

You will need a photo for a pass of three days and over (there is a very quick photo machine at the Morillon cable).  There are cheaper part-day passes (from 1130 it costs 166 francs and from 1400 it costs 100 francs) and there are sometimes special offers (such as the three days over Easter when a pass costs 360 francs in 2001).

A season pass only costs 2050 francs if you get it before 24 December each year.  Even if you are insured it is best to say yes when they ask you whether you want insurance – if you do have an accident it means that the emergency people will take you off the mountain without quibble and without asking for payment up front.