Driven to alps many times, cost wise 2 people = breakeven. Driving on French motorways is a pleasure, only queues I have ever encountered are once getting off the motorways.
Things to consider: Snow chains are a must as Gendarmes will not let you up the mountain without if snowing.
As above you get extra days skiing compared to time off work. I work in central London, generally we leave directly after work, go via the tunnel and arrive in resort (Tarantaise) by 8am ready to ski.