The most common impedance in actual practice for the sort of transmission line you have in mind is 75 ohms, not 50. Most of the cable TV network, and thus cable Internet, runs on this. That's why RG-6 and RG-11 grows on trees.

There is no big secret behind all of this. Transmission lines by definition have some impedance. Practitioners long ago adopted a handful of standard values that suit the common use cases given prevailing constraints, mostly driven by cost.

For things that transmit to the air (antenna feeds), 50Hz is the standard, not 75.

For even lower loss, ladder-line is available in 450 ohms.

Which is the only replaceman open-wire feeder at 600 ohms. They don’t make it any longer, you’re on your own to construct it or make-do with ladder line.

Yes you can definitely build your own ladder line. The insulators are available. But it's probably easier to use window line [0] instead.

[0] https://www.trueladderline.com/blog/window-line-open-wire-fe...