Damn, it looks like I've screwed up the product number. I meant Mogami 3367. This one should be around 2-3 euro.
You sure? Seems this one indeed is about 2-3€, but is listed as an installation cable, with solid core wires.
There are lots of options for high flex cable, however I guess it depends upon what you mean by high flex! The suppliers ot industry have all sorts of cable types for use in automation including drag chains and other mechanical contrivances. Examples:
https://www.l-com.com/ethernet-cat5e-cmx-rated-hi-flex-fr-tpe-jacket-double-shielded-2-pr-str-24-awg-1000ft-teal?gclid=EAIaIQobChMIxoDJu_KD8AIVuhatBh1PcwInEAAYAiAAEgJRufD_BwE
https://www.automationdirect.com/adc/overview/catalog/wiring_solutions/bulk_multi-conductor_cable/continuous_flexing_industrial_ethernet_cable
https://www.gore.com/products/ethernet-high-flex-round-cable. Gore has produced some very interesting cable assemblies over the years so you might want to try them first.
Thats what I have already commented. Cable, that is soft and very flexible, is a completely different thing than a cable, that is designed to be flexed repeatedly. The latter usually being cables stiff as a garden hose. They can be repeatedly flexed, but they are not soft.
There are plenty of others. It might pay to call an applications engineer at a larger wire manufacture and simply ask. As you have already noted some of the industrial stuff has a pretty rugged external sheath, you may catch the right adviser willing to forward forward you to a competitor that has something more like you are looking for.
Eventually you will be lead to somebody with the cable you need.
To go around calling companies, that is like an utopia. As a small company or an individual, nobody will talk with you. You are not worth them to even respond you to an email. And if you are, they will of course market you the most expensive (or with most margin for them) stuff they can find fits.
If you have a different experience, good for you then. This is just how thy business works. Meanwhile I have contacted two local distributors, that had some cables I wanted and how many of them did respond with a quote for 100 m roll? Exactly none. Then I order from Reichelt some cables quite on the expensive side, pay premium shipping of 15 € (which really is expensive, for just within EU two countries neighboring) and then after almost two weeks, the cable is not shipped yet? And I have specifically ordered one which they claimed they have in stock?
Welcome to the business of the second fifth of 21st century.
And then go figure, why almost everyone that can, does business in or with China. These folks almost always respond to questions and give quotes and they like to make a deal, unlike western companies, that are just after your money and delivering the product has low priority.
Sorry, I got a bit carried away, but there are things in the western world, that really pisses me off. Look, I would like to support local businesses, but in most cases, you simply can't, they just don't want to do the business with you.