How much are plane prices?

I'm looking to organise a music tour to Vienna for next summer (July 2012). We have to fly from the north of England, and as a rough deal I looked at Manchester-Vienna, which was �276 per person return for July 2011. If I was to get the tickets long enough in advance (i.e. November) would they be cheaper than this? We would all need to have luggage in the hold too. In addition we will be flying about 20 people, if I was to buy that all at once would there be a discount?