Follow this step by step procedure if you want the same inexpensive Christmas balls for your tree.
Step 1. Blow a balloon.
Step 2. Cover it with yarn.
Step 3. Mix glue with water. Add glitter for added design.
Step 4. Wet the wrapped balloon in glue mixture.
Step 5. Hang to dry for 24 hours.
Step 6. Pop the balloon.
This is how the yarn balls look in my new 6 feet tall (not yet done) Christmas tree.
Here's a close shot of one of the DIY balls.
One can actually play with the design for this project. Use different colors of yarn like red, green, or gold. Follow an overlapping pattern when wrapping the balloon. Aside from glitters, you can also decorate the balls with sequins or studs. Just have fun!