Given how overall cheap it is to actually make these things I have a couple suggestions to make to help balance them.

1) Increase the building size by 1-2x in width. Reduce the internal space to around half the vertical currently available (I'd suggest just enough space to have a single line of furnaces (Based on stone furnaces) cranking out goods given it's still an overall reduction in space). Reduce the side and top inputs to two each.
2) Reduce the cost of the initial building by about 20-25% on the stone bricks (Around 300-400 would be ideal). Reduce the power allowance from 50mw to 10mw.
3) Add additional tiers of buildings that increase by 1-2x in height compared to the original and allow for an additional set of furnaces (Again, based on a set of stone furnaces) to be set up each with one more input line on each side and top. Allow more power in the larger structures, balanced as needed against the original. Balance materials as required compared to the original.