RCA Phono Interconnect Under $400

when I bought my long tonearm, the maker essentially insisted I buy this Ortofon

I did, but frankly I do not hear any difference comparing several, including inexpensive one, Acos Lustre's OEM or Custom Pine Tree cable I had made.

I would say, buy from a source that accepts returns, try, keep or return.

I changed my interconnects to Locking RCA connectors

these, or others

If you cannot find ready made, you could have Pine Tree make you a cable: rca/rca/ground/locking connectors, your desired length.

I bought two of these 3 wire Component Video Cables, got 3 pairs of locking and each pair it’s connector’s a different color.

As others have said, buy a separate, or get a spool of green coated wire and make a separate ground wire with crimped spades.

https://www.google.com/search?q=green+ground+wire&rlz=1C1JSBI_enUS1081US1081&oq=green+ground+wi&gs_lcrp=EgZjaHJvbWUqBwgAEAAYgAQyBwgAEAAYgAQyBggBEEUYOTIHCAIQABiABDIHCAMQABiABDIHCAQQABiABDINCAUQLhivARjHARiABDIICAYQABgWGB4yCAgHEAAYFhgeMggICBAAGBYYHjIICAkQABgWGB6oAgCwAgA&sourceid=chrome&ie=UTF-8

I own a Zu Xaus that I've been very happy with, and their current Mission Phono is in your price range:

I’ve been using these excellent and reasonably price pure silver interconnects for more than ten years now, and have recommended them to several other very satisfied users:

Visit their website for links to several reviews and many user comments.
 

Review for Stager phono cable:

Just to point out that the video cables almost certainly do not have separate and equal conductors for audio hot and audio ground. In my experience that makes a difference. In cheap 75 ohm video cables, most likely audio ground is carried on the shield which therefore must be connected at both ends.