http://www.rdlnet.com/a_mix.htm - These look like they could be cheap, though they could also be hideously expensive. Someone else would have to name the impedance you want. I'm talking the 'STD-' models.
Things like these are punting around on the cheap; yes, it's a lot of features you don't need, but it has 4 inputs and perhaps the hope of a line output. If you can get one on special somewhere for $9, do the extra features matter?
Anecdotal evidence suggests most people do use plain old nests of Y adapters, not that I'm advocating such.
