Musubi with UmeAnother 6 key macropad based on the 6 Pack running an Arduino script.
This is also under 100mm x 100mm and you can get 10 PCBs for $2 from Easyeda.com. Combine it with other items to spread out the shipping cost.
Other PCB's that qualify for the $2/$5 10 PCB discount:
File on github.
White silkscreen rice and green solder mask nori. Red G20 ume.
White nylon M2 spacers and screws. PCB mount switches are required.