Shonkbot is an attempt at a very cheap educational/drawing robot made entirely from bits you can buy.
Matt, Anton and I schemed it up on the way back from Maker Faire UK 2015. It was a long drive. We had a lot of time for scheming.
Code for this drawing is on github
Parts for this version amount to about £7:
One old CD
Two 28BYJ-48 steppers with driver boards from ebay
Cheap Arduino Nano clone (could be replaced with a Shrimping setup for more cheapness)
3 x AA battery box with a switch
Cable ties for casters
wheels (with bore drilled out to 5mm)
Gluegun to stick it all together