Thanks for the replies. As you can probably tell, I'm new to this. Did a google search for "SATA power cables" and got a bunch of results for what looked to me like 4 pin molex connectors. The same thing happened when I searched both Amazon and Newegg. Now that I know what to look for, I should have more luck finding cables to purchase.
Your PSU should have SATA power connectors (if not, you can use molex to SATA adapters). So it's only the data cable you should need to buy, and only if your motherboard/computer didn't come with any (or too few).