BLU has been making some respectable low-cost unlocked phones over the last few years, and you can get your hands on one for cheap today. The BLU Vivo Air is on sale for just $150 on Amazon (that's $50 off). This deal ends at midnight on the west coast, so you'll want to decide soon.
The Vivo Air isn't a premium specced phone, but the design and build quality is rather nice. According to Cam, you'd never guess it only costs $199. So for $150 you really can't go wrong. The Vivo Air has an octa-core MediaTek processor, 1GB of RAM, and a 5-inch 720p AMOLED screen. It runs KitKat, but it's slated to get Lollipop soon.
It doesn't have LTE, but there's HSPA+ support on all North American GSM carriers. The phone comes in either black or white with Prime shipping.