You probably have been there already and should give some feedback. I provide here some background for later reference.
I do not know specifically about Val Thorens but I can give an overview of budget for skiing in the French Alps, I think it could apply to any resort there.
First, ski pass, accommodation, equipment renting are the biggest budgets. A ski pass is usually around 200 euros a week. Housing varies but it is not so cheap. I would say renting equipment is around 10-15 euros per day.
For everyday budget, I consider you have access to a minimal kitchen where you stay. If you want to reduce your budget, make your own sandwiches and cook in the evening. In a restaurant or sandwich stall a sandwich would cost probably around 7-8 euros and a main course would be around 10-15 euros, add almost 5 euros if you want a drink with it.
But even making your own sandwiches could be expensive: prices in resort's supermarkets are rather expensive (I would estimate 20% more than a quite large supermarket anywhere else), plus things are sold in small packaging, so the best idea would be to buy the more you can before getting to the resort. If you have a car, take advantage and buy everything before getting up to the mountains, just buy bread in the resort. If you don't have a car, buy the more expensive and light stuff, like ham/meat ...
For those hanging out, expect beers/drinks to be expensive too. I think you should expect 5 euros for a bottle, probably 7-8 at least for a pint in a bar.
Overall, the basic tricks are to buy food in the valley (Chambéry for Val Tho), especially if you have a car and then cook/prepare sandwiches for most days. But anyway, going skiing is quite expensive so be prepared to spend some money.
