A beauty, and new to me: the NRI-832 kit computer (by the National Radio Institute, for a correspondence course) has an 8-bit CPU built from 75 TTL chips, and has a visible ROM on the front panel: 16 bytes of toggle switches. You have 1 byte of RAM, expandable to 16 bytes. All this for just over $500, and in 1971.
Josh Dersch writes about it: http://rottedbits.blogspot.co.uk/2013/0 ... i-832.html - notice that the toggle switches have all gone missing in this case.
More info on the machine with photos of the insides at
http://www.oldcomputermuseum.com/nri_832.html
There's a Javascript emulator by Paul Robson at
http://www.robsons.org.uk/nri832/
which has a cunning extension to allow several pages of RAM and another to allow one level of subroutine call. He blogs about developing the emulator and provides full sources and documentation at
http://nri832.blogspot.co.uk/
where we see that he's ported it to C, put it into an Arduino, and now has a physical emulation. Video here:
https://www.youtube.com/watch?v=wvy4-w4MxtE
For a not entirely dissimilar idea from the same timeframe, see the Kenbak-1
http://en.wikipedia.org/wiki/Kenbak-1
one of many machines to aspire to the title of first personal computer.