It's been slow coming, but the Lumia 640 is a great phone. I'm upgrading from a Lumia 521, which was less than $99 (now around $50). That 521 is a great low-end smartphone, but I was ready for an upgrade.
But the 640, despite it's low price, is anything but low-end. If the camera is really important to you, you might need to upgrade, but the 640 is more than adequate with an 8MP camera and flash. It has Glance and the latest Windows 8.1 Update 2 and Denim. Also has NFC and VPN setup. Also double-tap activation. Comes with 1GB memory, but that's plenty since you can add an SD card for all the storage you'll need. Has wireless calling and LTE.
Since I'm into the Windows PC ecosystem, it was great seeing the phone sync with all my calendars, contacts, and apps.
Of course at this price it is plastic, but with a protective case, who cares!
A friend was examining my 640 yesterday and wondering why her smartphone cost hundreds of dollars more. Me, too.