This Pi-based model from TexElec is the one I used, but it's based on an open-source project that can be put together for much cheaper (I'm just lazy). I had to fiddle with settings a bit to get proper display, but it was pretty much a plug-and-play experience otherwise. I also have a magical Extron box I've yet to try, but it's long since discontinued and I was lucky to stumble across it at about half of its normal used price.Interested to know what eta/cga adapter worked the magic for you.
RGBtoHDMI