It used the same processor and 'only' twice the RAM.
Even assuming the RAM is the most expensive component, by definition, the materials cost no more than twice the cost of the original Macintosh. (~2500USD in 1984)
Of course, the Blit is just a terminal pulling applications down from a Unix host over the serial port; when you consider that the Blit is just a display, it does indeed seem a bit pricey.
