Best RCA interconnect up to ~$100?

For really well designed, high quality parts, hand made cables made with pride and passion for the Audiophile space, check out Pine Tree Audio.  Call Jessie and he’ll recommend the design best for you based on your sonic preferences and system.  Check out Pine Trees site, read some of the reviews and do yourself a favor and call, tremendous value and you won’t need to upgrade down the road. 

OP,

I have used and can recommend: DHLabs (not White Lightning), Morrow Audio (50% sale right now), Supra Cables Trico or EFF RCA cables (dealer selling on eBay), or Pine Tree Audio which are showing promise. All could get you a very nice RCA pair that will grow with you through to "mid-fi". A couple might cost a little over your $100 limit, but only by $20 or $30

I use Cardas Headphone cables on my Sennheiser HD660S and really appreciated the improvement over the stock cable.  Their Parsec IC should be of interest.

+1 for Blue Jeans Cable.

I was firmly in trenches in the ‘wires don’t matter camp when I had a friend come listen to my system running SVS speaker cables. He was very polite commenting about the transparent sound stage, but lack of detail. It left me ready to go amp shopping until someone asked what speaker cables I was running.. I ordered and installed a pair of Anti-cables.. much more detailed, spacious with precise placement.. just goes to show you don’t know what you don’t know!