We were in the alps in 02/03 and 03/04. I was on £70 a week as chalet staff (not MW), my gf was a nanny for MW in the first season so earned slightly more I think £90. Obviously accomodation, lift pass (usually only a resort pass on your first season) and ski hire is included in your package (oh, and tips, but most UK tourists are tight as). There is usually a small retainer/bonus built in if you complete the season. It really doesn't vary much – there is a vast pool of applicants to be exploited, so no need to pay more money.
Edit to say – the better paid jobs tend to include less time to ski. Gf only skiied on her day and a half off, where as I had 1 day off, but could be on the slopes by 10:30ish to 4:30ish each day if I got a move on.