BrachioGraph is an ultra-cheap (total cost of materials: ~€14) plotter that can be built with minimal skills.
At its heart is a Raspberry Pi Zero and some relatively simple custom software, driving three servo motors.
The mechanical hardware can be built from nothing but stiff card, a pen or pencil and some glue. The only tools required are a ruler and a sharp knife.
Almost everything required can be found in a desk or kitchen drawer. The entire device can be built with no special skills in about an hour.
The full documentation of the project, with detailed instructions on how to use it, can be found here