Upgrade Rel speakon cable

I have Zikhmark's upgraded REL cable on my R505, and find it way superior to the stock cable. You will immediately hear deeper, tighter bass, and it gets better as the cable breaks in. No brainer at the price. I have no connection to that seller, just a customer who likes the cable FWIW.

Cardas makes one as well. Pretty good & under your budget brand new.
Do a Google search & you should find the details.

The Synergistic Research Tesla REL Spec series hi-level cables are an incredible upgrade for any REL. More expensive than the others but definitely worth it.