Skiline had deals for apartments which included eurostar from euston, and ski passes and were under £500. No idea what the ski passes were (i.e. full area or not) but would be worth a look. https://www.skiline.co.uk/ski-holidays/eurostar-train
There is a bubble goes up from brides les bains to meribel as well, another option. Seem to remember there being a pub or two that had a bit of an apres vibe in brides as some of the instructors and workers live down there.
Aime could be an option for la plagne but the bus would be a pain (IMO) and probably not much of a saving when you add it up and include time wasted.