The problem with arranging a group trip involving anyone other than close friends is that you (as the organiser) can easily be left out of pocket or worse if things go wrong; people can and will cancel at the last minute, pull out without telling you, miss their flights, trash their rooms etc. leaving you with the liability. That's why I'd recommend using a UK-based (and ATOL protected) package tour company to take care of flights, transfers and accommodation, letting you focus on your studies. They'll be able to take payment directly from the other participants, meaning you're in no danger of paying for someone else's holiday.
If you start looking now at package trips for winter 2013-14 you'll be able to get an idea of prices. Start by looking on the websites but don't be afraid to call up in search of a good deal; if you can bring 15-30 people along they'll love to talk to you! Things to consider are:
- Transport - the larger tour companies will organise flights and coach transfer to the resort
- Accommodation - typically twin/double rooms; you'll want chalet/hotel style close to the slopes and the bars
- Food - getting catered accommodation (breakfast/dinner) means not having to deal with 30 people's different requirements
- Resort - pick somewhere large that can cater for everyone from beginner to expert skiers. Large resorts also tend to have better (or at least more varied) apres ski and nightlife.
A tour company will also be able to get you good deals on lift pass, equipment hire and lessons without tying everyone into the same option - you'll have people who want to hire expensive kit, or bring their own.
Assuming you're travelling during the university holidays, you'll be competing against other students for accommodation, so the earlier you book the better. You're unlikely to be able to get commitments during the summer vacation, so aim to get the booking confirmed during the first two weeks of September - any later than that and resorts will fill up fast for the Christmas/New Year holiday, although you have a bit more leeway if you're planning an Easter trip.