My husband gave me a hard time about getting this game set up for the party - he thought I was going a bit overboard - but it ended up literally costing less than $20 to make and took no longer than 30 minutes to set up. It ended up being a favorite activity at the party so it was totally worth it!
How we made our Quidditch game:
We compromised a bit. Instead of putting hoops at both ends of our field, we only put hoops in the middle of our backyard. We were afraid that if we put hoops near the fence, balls would constantly be going into our neighbors' yards, so we concentrated the game in the middle.
Additionally, each girl got a broom to play with. I purchased $1 dowels from Hobby Lobby. I collected sticks from our neighborhood and hot glued them onto each dowel. I finished them off with a piece of ribbon I had.
To play we used Flax & Twine's set of rules for the game here.
The girls really enjoyed it--even getting a bit competitive!
here, here and here.