Oh wow, you've really taken on a challenge with your first cosplay! To do the fan, I would get some big pieces of cardboard (Refigerator boxes are great for it!) or some thick insulation foam (the hard blue or pink kind, not the fluffy stuff!) and cut out the circle shapes on one layer of each. (I'd go with the cardboard, much cheaper and lighter.) Then, for the pole, you can either use the wood pole, or do a PVC pipe (those white plumbing pipes) which will be lighter to carry, and just cut a slit in the pipe to put the cardboard into it. Get some strong glue like E-6000 to glue them together, then paint.
Yes, they're cheap materials, but if you cover it with either fabric, craft foam, or even papier mache, you can make it look really good. Because you'll have to wear it on your back all day/carry it around the con/event, you'll want it to be light so you're not overburdened.
GOOD LUCK! 8D