Solid core XLR interconnect recommendation (up to 300$ for a used 8ft pair) ?

Build your own three strand braid like Kimber.

I’ve used this cable making my own braid and it sounds wonderful. Trick is not to braid too tight and keep consistent. Below is from Percy’s site.

http://www.percyaudio.com/Catalog.pdf

Michael Percy Audio.
Wonder Wire: A proprietary design high performance 19ga solid core, silver clad high purity copper with a unique crystal structure,Insulated type with a special high voltage (9000VDC) clear dielectric @$2.25 per foot Deduct 10% for 100'+ Wonder Wire.

NEUTRIK XLR: Gold or silver plated 3 pin NC3XB type XLR cable mount , black shell... $5.25 each Gold plated assumed if you do not specify silver (all 4p, 5p gold)

$120 and you’re there. Solid core braid is a little stiff but it works.

Want something easier check out VH Audio for bulk cable. If you don’t want to put the plugs on yourself I think Chris will do it at a fair charge.
https://www.vhaudio.com/wire.html

Might be be difficult finding a 8ft cable so look at building your own.

FWIW, the whole point of balanced line connections is to eliminate the artifact caused by the cable.

This has as more to do with what is driving the cable than the cable itself. As long as the cable is built correctly (twisted pair within a shield) and it is driven correctly, it will not have a sonic artifact, solid wire or no.