Just found this interesting thread on Amiga.org about a guy who is thinking about making scandoublers. Here. The thread is still current but hasn't had any update as to when and how much the scandoublers will cost. Also it's not what you'd call compact but if it works then great.
Just looked around and it looks like he's also done a similar post on Amigaworld.net.here. I almost feel left out as he seems to have forgotten about us.