Here follows a list on how your event could be more "open" and definitely cheaper.
The Open Source Event Planner manages her/his project with WinPlanner, BaseCamp, Auto Project Planner (which automatically calculates start/end dates) or the minimalistic airToDo.
Office is a thing of the past as OpenOffice performs at the same level with no costs.
Team management could be mastered also via Group-Office Groupware a nice Internet/Intranet tool.
As always mail me should you have any question