I don't know if it would fit your needs, but check out RiseVision for a no-charge signage solution. They also sell hardware, but that's not a requirement to run their software for free as the source of your signage. They have software clients for Linux, Windows and Chromebook and you can find 3rd-party apps on the Play Store to run on Android.
I'm still looking for a nice, inexpensive Android Stick to hook up my account to a TV. So far, I've tried it on a Windows PC and a Nexus7 and both work great.