$50-$100 worth of kit? The dongle is €10 (21% VAT incluis) in an Apple Store. EarPods with lightning connector integrated are €23 (again, VAT included) if you want the most easy solution on a like €600 minimum phone.

If you have a phone that doesn't come with a 3.5mm headphone jack, then you're able to spend €10 on a dongle to make your $4 set of 3.5mm headphones work. If you cannot afford that, then you have one of the many phones that do have a headphone jack. I'm sure that, if in the future everyone for some strange reason got rid of the integrated headphone jack and there's no company that sees it as a USP while people still want to use 3.5mm headphones, that the price of dongles will be next to nothing.