My own design.
This DIY tDCS works with a 9v battery.

about tDCS: http://www.radiolab.org/story/9-volt-nirvana/

-M3 screws 40mm x2.
-M3 nuts x2.
-banana connectors x3 (generally you only need 2, but in case of multi electrodes use I put 3 holes).
-cables with banana plugs for the electrodes.
-300ohm pot (can be quite hard to find...)
-3mm LED (5mm should also fit).
-about 10 or 15 ohm resistor x1
-a resistor for the LED (1kohm should be fine with any kind of 3mmLED)
-5ma amp meter (Ebay...)
-a power switch (14mm*10mm)

Wout can print the enclosure with any plastic.
ABS do not goes well with water, thus I suggest you print the electrodes with PLA.
the PCB is inserted without screws into the upper part of the enclosure, use sandpaper to widen the slit if needed.
the LED is bonded to the upper case with a glue gun.
Use superglue to bond the 2 parts of the electrodes. once bonded, they are fairly strong, not so easy to break.
you can use the Stainless mesh from a "tea ball", those are very inexpensive, widely available and easy to cut with regular scissors.
then you just have to cut a cellulose based sponge to fit the electrodes (thickness is about 6mm, bread knife works well to cut sponges, but good luck with that), or find a 6mm thick cellulose sponge.

Have fun!