Best RCA interconnect up to ~$100?

+1 on Darwin Cables. Right now, on their Specials page, they have a pair of their entry level Silver 1 RCAs for $195. You really can't do better at that price.

All the best,
Nonoise

Usually anything silver I like best between electronics, although an interconnect manufacturer told me that copper was best between a preamp and subwoofer as copper does better with bass than does silver.

A friend in NorthCentral PA made his own silver interconnects, called them ‘Blasphemy ICs’ and were some of the thinnest most reasonably priced silver ICs I ever saw.  They sounded phenomenal!  I bought many pairs over the years, and then gave them to friends or sold them with the gear that I sold at the time.  At one point, I was using all of his ICs in my system for several years, as I change gear pretty often.  You don’t need to spend tons of money to get great ICs.

Custom 

You can chose every component. I just had some balanced interconnects made with solid silver and the exact XLR connectors that are in my Luxman amp.

still kept it under $150. His builds are so well put together I’ve almost entirely switched. 
 

https://www.prosperhifi.com/