Homebrewed Macro Keyboards?

MightyMaus asks: "So I've been checking out various hardware websites lately, paging through computer retail catalogues, and basically pining for a better-paying job. But one device that's really caught my eye is the Programmable Keypad. Looks pretty cool, but $140? No way. Even the smaller version carries a hefty $90 price tag. Now, it seems like making one of these should be relatively easy; but the almighty Google returns nothing but more places to buy these things. So where do I turn? To Slashdot. Has anyone hacked together one of these before?"