I got a super bargain on insulated firebrick for my masonry heater core!
I am lucky enough to live within comfortable driving distance of a (sadly dwindling) ceramics production town, so I thought to call a salvage yard in the area to see if they had any kiln bricks sitting around. They had six boxes of deadstock Isolite LBK-30s sitting around, about $2.50 a brick vs $17 ordered from the manufacturer. They're rated for up to 2800°F