up my Optoma 739 front projector and am in need of running a 25 ft cable for audio to my receiver. Any good place to buy a reasonable priced coax digital?

What would your front projector be doing with audio?

I didn't want to run a video cable in 25ft length so I mounted the Oppo next to the Optoma.

cost: $20 or less

Coax is rather prone to inteference from outside sources with that sort of length. It'll cost a bit more than a coax run, but the results will be better. If you have to go with coax, Matt Devo has the right idea. Use quad shielded RG6 with the F pins at each end + RCA adaptors. If you know how to solder, just solder RCA plugs to the RG6 without the F-pins (solid core to center pin, braid to outer plug). Make sure it's RG6 and not RG59. RG59 is okay for component video, but not good for digital sound.

It will work probably if you have a glass cable with good termination. I don't think plastic will cut it.

There's the higher quality multi-strand plastic optical fiber version for example. Details should be on the packaging when comparing cables.
For those wondering, TOSlink is an optical cable. TOSlink is short for Toshiba Link as they were the originators of the optical digital audio connection.

I wasn't saying it wouldn't work just that you need decent cabling. Technically the TOSLINK spec was only for 10 meters so you are right at the specifcation limit. Personally unless there was a ton of EMI floating around I would just use coax.

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