[Greg Needel]

I think the number can greatly depend on alot of things. FIRST will give their fields to you for free to use, but you need to take out an insurance for them I think $50,000. Also you need to pay the shipping to and from your event. In some cases this can be reduced by partnering with other events in your area assuming that there is somewhere the field can be stored. Additionally to this they also don't come with the disposables (tape, zipties, glass cleaner etc).

From the events I have been involved in the most costly thing is getting the field.

Also you need to figure the costs of facilities, food, security, janitorial, and many other admin costs. The big battle really comes from how many teams you think you will have and how much they will pay to come to your event.

Also the timing of your event is important. During summer it can be difficult to get things organized and to get teams to show up. During the fall there are lots of off seasons and you don't want to subtract from another team's event if you will be inviting the same teams.