3rd Party Seller through Amazon Prime has the Doss Cloud Book Wi-Fi & Bluetooth portable speaker for $20 shipped. [amazon.com]
Looks like a book. Sold for $70 Previously.
Available in lots of colors [amazon.com]
Has bluetooth, but what makes it different from other cheap speakers is that it also has Wi-fi, which lets you hook to Spotify Connect, Pandora, and any DLNA music you have on your home network. (In most cases you need a premium subscription for any of the Wifi speakers to work on Spotify/Pandora).
I have never heard one, but I have owned Wi-Fi speakers from Que, GGMM, & Audio Pro that use the same wireless system called LINKPLAY. [linkplay.com]
It is a poor man's chromecast audio (which is a poor man's Sonos). It does most of the same things but not quite as well. I use mine mostly for Spotify which works fine.
You can use 2 in the same room for stereo. Or you can sync them in different rooms around the house to play the same thing.
SD thread of an early deal on the Que Speaker that uses the same Linkplay system here.
$20 is quite cheap for a wifi speaker. You can use any of the Linkplay apps if you have other speakers.