I think that the reason the restaurants were so expensive was due to the exchange rate - when we went, it was about 1.45. It is much better now. Other than food, the prices were fairly reasonable. Our lift tickets for 6 days for 4 people (2 adults, 1 teen, 1 child) were about 800 euros total, and our accommodations were less than what we normally spend in Utah or Colorado (we stayed at a VRBO apartment). Chamonix has a whole variety of different types of places to eat, so you don't have to spend a lot if you don't want to. We spent a few nights getting pizza from the pizza cart near our apartment, or take-out sushi from the place next door.
The management company of our apartment was able to buy our passes and have them ready when we checked in, but I think it's probably pretty easy to buy them on site. If you are staying at a hotel, the concierge can probably get them for you. When we went to St. Anton, we requested them there and the concierge presented them to us on arrival. Have a great time! Chamonix is so much fun!