Single ended vs Balanced output performance/sound difference is a function of your DAP, not IEM. I assume you never tried 4.4mm HO in your ZX300 since you are asking about the difference? Cables can/will get price depending on the material, number of conductors, and a brand name. You wouldn't expect a basic copper wires to cost the same as silver plated copper or pure silver or gold plated silver, the same as you would expect a price difference between necklaces, buying jewelry for your wife/gf
You can go with
64 Audio premium custom cable, and configure it with 4.4mm termination, that's a budget friendly route.
Regarding ZX300, not familiar with it, but WM1Z I have access to now was designed specifically to give you better performance/sound from balanced output. Though the latest fw update made 3.5mm sound better, it's still not the match for balanced 4.4mm output.