The substrate is the little PCB that the four dies are placed on. Simon is saying that they can place the cut dies on a chip for $20. Making boards will cost significantly more than that.
But still less than half the current cost, that again, is an interesting proposition. And again, the cost of the PCB was irrelevant back in January. They never let us pay for it, they preferred to lie about not being broke.
Edit: I knew that checking the dockets on a Saturday morning would have resulted in interesting stuff... The motion for the sale to liquidbits is there.