You won't need any expensive tools or supplies at all. Most can be found around the house. You will need:
1 expo marker
2 nerf darts
1 bic pen
Some thin cardboard(gift boxes work the best)
Step 2: Gutting The Expo Marker
You will need the scissors or a tool to pull out the back end of the marker. I used scissors to wedge it out, and it worked pretty well. After, take your pliers and pull out the felt tip of the marker. Take that, the end, and the piece inside the marker and throw them away. You won't need them anymore.
Step 3: Making The Barrel
This step is very similar to the previous one, but you're doing it to a pen. The pliers are a good tool for this one. Once you have pulled it apart, all you will need is the plastic shell. Place the shell in the expo marker so you can see how much extra pen you have. Cut off the remains.
Step 4: Padding.
This one is a tad confusing, but bear with me. Take a piece of card board and cut it the size of the pen. Don't make it too long, because you will need to roll it up. Once you did that, roll it up working it around a little. You should have a roundish tube when you are done. Place it in the marker tube, and trim it if needed.
Step 5: Nerf Dart Time
Take the two nerf darts, and pull the heads off so you have the orange pieces( yours can be different color). Take the pen shell and slide it inside the foam cylinder. You will notice it's too small, that's why you have a second dart. Place that one on, and cut off the extra
Step 6: Assemble!
Take the nerf tube you made and slide it into the marker. The cardboard tube should be in the marker once you slide it in. Work it around a little, and make sure it fits.