Excellent work, Ngzhang!!
Speculation on price; Those particular spartans are $158 for <60, the boards have a LOT of components and the PCBs not cheap. High amp regulator $30+. Maybe saved a few bukcs on a low end uart? Not seeing it but am not real familiar with them. Not sure if he has a license fee attached but will add it in case.
builders markup included result = XLX $386, PCB+License $145, Components $110, usb and power cable $7
= ~$648 or $1.80/MH
Did I miss any thing?