Max has something for you. Let's Make!
If you want to build a fun, affordable, safe(ish) arsenal, then begin by gathering your supplies:
foam... pool noodles are great, and can sometimes be found in the thrift shops, and yard sales
2 part epoxy
hack saw, and utility knife
access to a circular saw
Duct tape... lots!
*Geoff, Alex, Suki, and Grant were at Burning Man, together, in 2011. I made Geoff a long white, silk tunic, and at Burning Man he was charged with defending the Trojan Horse, and keeping spectators from being crushed under the 50' tall, 28 ton moving art piece. He carried his foam and duct tape cudgel to exercise his authority, and can be seen near the massive wheel, 45 seconds into this video. (I cannot suppress my delight.)
Remember, measure twice, cut once.
Max decides on the general idea of his weapon, this one will be a short sword. He's measured his PVC, and is marking it to cut with the circular saw. He is accounting for the length of the blade, as well as the hilt... leaving plenty of room for the thickness of the foam and a comfortable grip on the handle.
Time for the disclaimer: Don't be a goof. Play fair. Play nice. Do not pummel, harass, abuse, maim, harm, terrorize, intimidate, or hurt your frenemy. Now, go play, tinker, and Make!