Hmm, the Apple I was essentially a bare-bones PCB. I struggle to imagine a CNC-machined piece which would convey the essence of the Apple I.
The unpopulated Mimeo PCB costs $170 (plus shipping). For my taste, buying one of those and framing it behind glass would produce a "minimal" Apple I exhibit to hang on the wall. You could always reconsider later, and buy the components to populate the board. If you are not obsessive about obtaining components with the correct vintage date codes, and just want something that works, the chips should not be too expensive. (There are a couple of rare chips, I believe, but mostly plain 74 series TTL.)
And, of course, building something to hang on the wall vs. building a working unit does not have to be a contradiction. You could consider building a working unit in a picture frame. I recently completed my build of a PONG cabinet, which exhibits an original 1972 PCB in that way, and quite like the result. For a wall-mounted computer, the keyboard may be a difficult decision -- either mount it vertically inside the frame, foir a self-contained unit, or use a wireless keyboard to make the unit more usable?