SPDIF Coax cable recommendation?

This is a little above your budget but will be worth it.  Read the reviews.  I was using a well-respected Apogee Wyde Eye but as soon as I put this in it was night and day better in every way.  Best of luck. 
https://www.usaudiomart.com/details/649932466-acoustic-zen-mc2-digital-coax-cable-1m/

I like the Acoustic Zen very much. Make him an offer.

Nordost Silver Shadow, Supra, then Canare. You’ll have to spend a lot more to better these cables. Supra in The States you’ll find on eBay and Canare many online vendors but most seem to go through Blue Jeans.The Nordost you can find here often.

I used a generic Amazon cable and then upgraded to DH Labs and lastly Shunyata Sigma.  Each step was a marked improvement.  DH labs was the best value.  They have a money back trial period.

I would advise to get the best you can under your perceived budget. $200(?)

First thoughts for under $200 would be something from Silnote, Audio Envy, Moon Audio, Zavfino, Morrow Audio.

Second thought if you wanted [much] cheaper (in agreement with AGD above) are the Blue Jeans cable, Supra, or maybe Mogami. If you could wait a few weeks for delivery (and didn’t have any other ’concerns’) - would be to try Chinese Nordost Valhalla or Odin knock-offs.

Good cable choices generally won’t usually turn a decent $5K system into a great $50K one, but lousy/wrong cables can turn a decent system into one that is just average - or worse, almost unlistenable. (Although admittedly a digital/SPDIF cable less so).