I recently wanted to setup a rear projection screen for a family event and almost fell off my chair when I priced out what it would cost to purchase one. After some googling I saw some posting where people had used sheets or something else that is semi-transparent, so I thought I would give that a try. I hung a variety of different things up in a doorway to test their rear projection capabilities and ended up using a $5 frosted shower curtain that seemed to work the best. Ironically a more expensive shower curtain ($15) did not work as well since it was too thick and didn’t provide enough light pass-through.
The light shower curtain needed something to force it to hang straight, so I used 2 thin pieces of wood I had kicking around (a long dowel would also work good) and simply wrapped the shower curtain around the wood once and then stapled it for strength. A couple pieces of wire attached to the wood provided a quick way to hang it. Some pictures are below of how it worked and is put together.
This is the screen in action. Was very crisp and bright:
Top wood support with wire:

Here is the bag from the shower curtain I used (cheapest one they sell at SuperStore):





Greeting from Australia. Thanks for the insights.
Thank you thank you thank you! You saved me $40 and much hair pulling on a sold-out-nearly-everywhere-this-close-to-Halloween hunt for a purpose-made fancy cloth, and the $4 shower curtain I picked up on your advice is perfect.