The SynPad is a position sensitive midi drum pad that you can build yourself using simple materials and tools for around 50 UK pounds (depending on what materials you already have, and how many pads you want to make.) The pad can detect where you have hit it as well as how hard, so that the synth it is driving can change the sound continuously as you strike the pad in different places.
The software I have written to make the sounds is currently linux based, but would not require much work to adapt to a windows or mac environment.
The skills you need are basic wood and metal work (cutting and drilling), enough electronics knowledge to build a simple circuit from the schematic, and a moderate amount of experience with making music on the linux operating system. You don't need any programming experience to start making sounds under linux, but would if you want to create your own synths to make different sounds, or to port the program to another OS.
If you have built one of these pads, or are thinking of building one, it would be good to hear from you.
Hope you enjoy making and playing this instructable!