This is a fundraiser that works best in October, giving you the opportunity to discover all of the haunted places in your neighborhood and learn something about their history.
Advertise the fact that your group is putting on a haunted tour bus ride, then rent a bus for this purpose. Get permission from all the places you want to visit along the route and get in touch with your local municipality to see if there are any restrictions regarding commercial drivers licenses.
If you can find a local historian or paranormal researcher for your tour guide then even better — ensure you have a PA system set up on the bus or a portable speaker system in place so that you can all hear everything that the tour guide is saying.
It's a good idea to work out in advance how you'll be stopping at each place. Don't forget you'll need to find a restaurant for lunch (you can include this in the price of the tour or let people pay their own way). Reserve tables in advance at your chosen restaurant and see if they will create a “spooky” menu that fits in with the theme of the day.
As a final touch it's a nice idea to put together a souvenir map, including details of each stop, that participants can take home with them.
You can find more Halloween themed fundraisers here.