I think it depends on the brands you buy honestly. Some brands rarely go on sale anywhere, and those brands are not higher at Zappos. Keens come to mind.

OP, seriously how did 6 pairs cost $400 anyway? Even $50 is on the high end for kids shoes, and that would only be $300...

If you want a deal, order from shoebuy.com, they offer the same shipping deal as zappos but if you're on their email list they'll send you special offers all the time. The tradeoff is that shipping is slow. If you want super quick service order from zappos. Sometimes the merchandise overlaps but not always.