The PLUGIN synths available in the webshop are already cheap at $19.95
However they are built on SMD chips not easy to solder for the normal hobbyist.
But now there is a through-hole kit for DIY.
The kit contains a USB PCB and a preprogrammed chip.
The chip is programmed with a simple basic drum kit.
Built on V-USB technology the kit is available for $9.95
Here is the PCB and schematics for the stick.
IC1 Preprogrammed Synth Chip
R1 22ohm resistor
R2 1.5Kohm resistor
R3 680ohm resistor
R4 174Kohm resistor
C1 100nF ceramic capacitor
C2 10uF electrolythic capacitor
Z1 3.6v Zener diode
CLB1 1 meter USB cable
CN1 3-pin Stereo 3.5mm Jack
PCB1 DIY Synth Stick USB PCB