https://www.aliexpress.com/w/wholesale-lc-apc-invisible-cabl...

I can second this 0.9mm transparent stuff, I've run it successfully and it's very subtle.

Depending on the media converter pair you're using, you probably want UPC instead of APC. I also found that the cheapest generic bidi media converters tend to be SC, so I want with a 30m pre-terminated SC/UPC cable. Total cost (cable plus media converters) was about £30.

Alternatively, you can order a custom 30+m white 0.9mm cable from FS: https://www.fs.com/uk/products/12285.html Lead time is fairly long.