My son’s class did a cool economics project that involved quick and easy crafts. Each student had to create a product that would sell to students for 50 cents. They learned about producers and consumers, supply and demand, and value. It took us a while to find the right project for him and ended up making these Monster Corner Bookmarks (directions and template at I Could Make That; we simplified by just using one solid-colored paper). They were a huge hit! It cost us nothing but time since I have years of scrapbook paper on hand, and using circle punches saved a lot of trouble and tears.
At the fair, it was so much fun walking around seeing what all the third graders created. I especially liked the Angry Bird Ornaments in red and blue (similar tutorial from Dollar Store Crafts), and those were quickly bought by the kids. One young lady made Poinsettia Pens; I found a cute green version over at The Cutting Back Kitchen. There were lots of great bookmarks, and I loved these Santa, Snowman, and Rudolph Tongue Depressor Bookmarks. One of the most clever ideas was this Snow Measuring Stick, made similarly to this one at All Kids.
All of these are quick and easy crafts that kids can make to give to a friend or neighbor.