I constructed this for about $20!
10- 1"- 1/4" bolts
10- 1/4" lock nuts
20 - Washers
2- 55 gal plastic barrels (be cautios of former contents. find food grade, or soap)
Mounting hardware: I used a spare swing, and lag bolts and washers.
1/4' drill bit
ratchet and wrench
Step 1: Barrel Prep
Use the jigsaw to carefully cut along the inside rim.
Clean up the edge with sand drum on a drill or dremel, or an angle grinder .
Repeat with the second barrel.
Sorry for the lack of picture on this step, I did this some time ago.
Next do the same to the bottom. Be sure to leave about 1" around the edge to bolt together.
I used a screw and a sting as a compass from center.
Sand these edges very well so kids don't get scratched.