Some of them are just to a single yellow RCA and a S-Video.
Like
this one. Even if you can't find one like that you could use the S-Video plug on the kind you're talking about with a RF Modulator that has S-Video in, don't know if yours or the radioshack one I linked to has s-video, but I have one in a box around here somewhere that I've used for a similar purpose to yours so I know they exist. Cheapest would probably be to look at ebay a little closer for an adapter like I just linked. Assume you've already given it some thought, but for audio the simplest route is probably to get a 1/8" stereo to Left/Right RCA's at radioshack.