Simple, Cheap, and Effective Hawaiian style spearfishing gun.
Step 1: Materials
2 ft Rubber Surgical grade Tubing or Exercise bands ($3-5)
Small Section of PVC 1/2in - 1in in Diameter ($2)
1 Youth Arrow with safety tip ($3)
4 - Zip ties (.50)
Total cost for these materials should be less than 10 bucks, if not free. All these things are pretty easy to find.
Step 2: Assembly
Take both ends of the rubber tubbing and place each side evenly onto the PVC pipe. Once in place tighten a zip tie around the the rubber tubbing and PVC, leave around a 1/2 inch of rubber tubbing at the end. Now fold the tubbing back and place another zip tie. This should hold everything nicely in place. I added a few more zip ties toward the top of the PVC, just for good measure.
Step 3: Testing
Dry fire it a few times before you add the arrow. It will work similar to a sling shot holding the tail of the arrow in the center of the rubber tubing. Draw back and then release.
Please be safe!! I have a one eyed uncle that can testify to the fact that arrows are dangerous.