Scott has one Ninjago spinner that he bought with his limited spending money. He has wanted another one, but they are about $14 and he spent all his money on a Lego set at Christmas (in fact, he spent more than the money he had from Christmas and was in debt to me for the balance until he finally took a load of bottles back to the depot). He feels pretty certain that he's going to win $50 from the Lego Club, but we won't take that as collateral.
After examining his one spinner a little more closely, I noticed that we had several of these same pieces in his massive tub of assorted Lego that Grandma M gave him for Christmas. We set out to make some spinners of our own.
At first he didn't really understand the importance of symmetry in building something that is supposed to stay spinning for a long time, even after crashing into another spinner. But after I built him a few examples, he figured out a way to build his own. It was like a prison cell, and it was very sturdy.
Sadly, the name-brand spinners are weighted with metal inside and stay spinning longer than ours; however, we had a lot of fun making these and we managed to stay out of debt. I think it was a great move.