Kalman Reti, the Last Symbolics Developer, Speaks of Lisp Machines.

"We took about 10 to 12 man years to do the Ivory chip, and the only comparable chip that was contemporaneous to that was the MicroVAX chip over at DEC. I knew some people that worked on that and their estimates were that it was 70 to 80 man-years to do the microVAX. That in a nutshell was the reason that the Lisp Machine was great."

https://docs.google.com/file/d/0Bw4Wz8Ir0pl1cmNRaHYwdU1wdXM/edit

Source: http://www.loper-os.org/?p=932