Best Digital RCA cable under $100 new or used?

Termination is paramount! More important than wire type, really. 75 ohm Canare connectors are the truest. So, I would go with Signal Cable.

At $99, I found the Transparent Digital Link to be significantly better than other similarly priced RCA SP/DIFs I tried. It was smoother, more musical, less artificial sounding with more natural detail and bloom to the dynamics.

Apogee Wyde Eye. Canare connectors and true 75 Ohm cable. Found them to be very-very good. Could be bought from Sweetwater for below $100.

The Black Cat Veloce from The Cable Company is excellent and so is the Wireworld Starlight 6 and Morrow Audio DIG1. All three around $100 at the 1.5M lenght.

Thanks for all your wonderful responses. I spent some time reading up on all the cables listed here. I boiled it down to two: the Auricle Audio Standard Digital and the Black Cat Veloce. I went ahead and ordered the Veloce. I would like to order the AA Standard Digital and have a proper duel but I see nowhere where AA has a return policy.