With VIA, the cheapest normal one person fares are $145 return. VIA Rail do groups rates for groups of ten or more, and every 20th ticket is free (effectively) - see http://www.viarail.ca/en/fares/discounts/groups - but I've no idea hwo much you get off. You can also charter a private car (http://www.viarail.ca/en/resources/chartered-car-rental), but that costs around $85/person one way.