"Hobbyking has some 3 bullet/pole ESC connectors.  You could use those and eliminate the ESC signal/power connector completely.
This would allow you to mount the ESC's inside the frame and just run the three wires out to each motor.…"

"Can you elaborate on the cost of the arms?  $34 each (with the legs) seems a bit pricy compared to other arms on the market.  Is there anything special about them other than the high grade Nylon?  It also appears that the rail system is integrated…"