They arent super hard to build, just pricey. Kale wool and refractory cement to make anything in a truely useful size is going to cost a few pennies. A good bet would be to scavenge copper, melt and sell as a way to fund the operation. All of your neighbors throw out things with copper wound motors in them, lots of copper to be had if you dont mind doing the melt. The shit they coat the copper with comes off as slag in the pot.