Since the astounding success of Antsy Labs' Fidget Cube, clones have sprung up everywhere, such as the $3.78 Chirisen cube. I can report that one will last the weekend without springing an anxiety leak. A pack of six is $13.39, just two bucks and change for each one.
Update: readers point out not only that the Kickstarter original is still directly available from the inventor, but that the generic ones are likely to be Antsy Labs' own manufacturers ripping them off. So I've replaced the link to theirs with one to the real thing.
Richard Stack writes: "I have an actual FidgetCube and someone bought me a knock off for Christmas. The original is much much nicer."