Creating a Green Screen on a Budget

I have been trying different ways to create green screens on a limited budget. I found some pretty inexpensive shower curtains that I put over my classroom and library white boards but these leave gaps at the bottom and I can't have people's feet in the videos. I found this video on YouTube and am heading to Wal-Mart this afternoon! I am also going to check and see if the art teacher in my building has any plain green paper which might work just as well and the video below.