Not easy at all.
I've visited the website www.laclusaz.com but the only regular bus service it refers to comes from Annecy, which is not a lot of help for anyone coming from the other direction.
The only other bus I can find that goes even vaguely into the area is a schooldays only journey from Bonneville.
http://infotransports.cg74.fr/ ligne 71
There may be more buses during the ski season.
Trains from Chamonix and along the way to St Gervais, Bonneville, etc
Best of luck
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