How does Discount Dance Supply sell for so cheap?

A lot of it has to do with the scale of the business involved.

First, DDS has big buying power, so they are able to buy in large quantities. Usually when a merchant buys in large volumes, the cost per unit from the manufacturer goes down. The merchant then passes the savings on to the customers. DDS has 6 or 7 store locations, plus a popular website, so they have the capacity to move a large volume of merchandise daily. They very likely have a high overhead, but the volume more than makes up for it.

Local dance stores, unless they are part of a larger company, tend to have higher prices in order to make up for their expenses. In technical business terms, smaller local stores have a higher overhead ratio. Part of the reason for this is they can't move the same volume of merchandise as large companies, so their expenses relative to their size are higher. Small local stores generally also have a single point of sale, whereas companies like DDS have multiple points of sale, a major one being their website, so they have a broader exposure to the market.

This isn't just limited to dance supply stores, though. The same sort of things happens with electronics, sporting goods, etc. Big online merchants tend to have lower prices than local stores because their overhead to sales ratio is better. It's not necessarily the fault of the local stores that they may cost more--they are just adapting their prices to make up for lower volume and the cost of doing business in that particular county or state.

I hope this helps.