I need a SATA cable to hook up a new (to me) hard drive to the motherboard of a new (to me) computer. It looks something like this:

I found them online from a reputable retailer for $1.99 each. I bought two. The retailer has a First Class USPS shipping option that only cost me $2, so for $6 I have two cables on my way from North Carolina.

I stopped at my local Best Buy over the lunch hour to see what they have, and sure enough, they have a SATA cable in stock. (Probably the only place in town that does.) Their price: $19.99.

I rest my case.