A good inexpensive speaker that I use for this purpose is the Fabriq speaker. It supports DLNA and works well for TTS using the Generic Media Renderer linked to above. I use webCore to send voice events to it, but the Message Central smartapp referred to looks pretty flexible/powerful if you want to stick w/just using a smartapp.
The Fabriq frequently goes on sale for $30-$40, unfortunately is not on sale right now.