2 terra cotta pots (22 in, 18 in) - $88
Ceramic fiber mat - $31/meter
12 fire bricks - $54
80 lbs concrete slab mix - $3.97
Total = $180
*You might notice the original post lists the total cost at about €113, or about $120. Not only were the prices for materials different because they were in Europe—they also had access to some materials beforehand. This list of materials is assuming you're starting the project with nothing but a sturdy base for the rig, and some standard power tools.
Start with two terra cotta pots. Make sure the smaller one fits into the larger one with plenty of room to spare.