10 years ago I made this kids level project for the AMIGA:-
http://homepages.tesco.net/wisecracker/public/SCOPE.GIF
It was a real time AC/DC coupled Oscilloscope for the Classic AMIGA...
The cost to build it worked out to about 75 UKP in those days...
Just bought this today, 15-10-2011 for 80 UKP from MAPLIN...
http://www.hps140.com/
We have come a bloody long way in consumer electronics
in the last 10 years...