The forge took an evening to weld together, cost virtually nothing to build (all scrap metal) except for the $8 hair dryer and $12 dimmer switch.
When I first started out, I worked in a Coal mine that allowed employees to have free coal. Consequently my shop was heated by coal and made a forge too.
I can go to a coal dump and pick out my nice Obsidian looking, hard, shiny lumps and the #1 reason is... IT IS CHEAP!