To paraphrase the CK-12 mission statement, this site is here to help provide content for students and teachers and it is FREE! That is, like, the best price! Sometimes free resources are better quality than you would imagine. I have spent a few hours looking through the site and have to admit that I am impressed. You can search by grade-level, content area, and even by country! Here is a picture of what you can find on this wonderful site:
One site that I have found particularly useful when searching for free resources is OER Commons. This site allows you to search by grade level, subject area, and several other criteria. Heads up though, people who share the materials get to choose tags for their resources (I assume...) and so some resources you find may be tagged wrong (I found one claiming to be about Physical Science that was much more geared toward ELA). While not everything on here will necessarily be perfect for you, there is a lot here to consider!
This lesson could be adapted to many different situations.
This is kind of just a neat idea that anyone could use!