Have a look at the inside of an SR-71a.
Not knowing what 2x opamp + 2x buffer is used, I would say that I could prolly build one for around, oh, $300 with custom extruded case and laser engraving, and I would prolly ask, oh, $450 for my time, ideas, sourcing parts and R&D.
EDIT: I totally forgot about testing and customer exchange/refund policies, oh and shipping, on both sourcing parts and final product. This is assuming of course that this whole shebang is happnin in my garage/basement.
EDIT#2: Forgot, after finish and engraving the housing must be sent off for oven baking.