As for the very expensive, mostly standard layout keyboards... it's an expensive hobby with marginal improvements at best, but the same could be said about furniture purchases. Most people don't choose furniture based solely off its functional characteristics. They want something pleasant to look at, especially since it's something they're using every day for a long period of time. I think there's plenty of utility in that, though personally I would never pay the prices that these people do.
[1] https://www.reddit.com/r/ErgoMechKeyboards/
DIY can lower the price, but it is a hustle and in the time needed is not free.
Maybe at some point Logitech will offer a split one for a more reasonable price, but I won’t hold my breath.
How do I get one that I can pull out of the box and be typing within 60 seconds?
Pro'bly the most popular pre-built keyboard along the same lines is the Moonlander. https://www.zsa.io/moonlander/ The configuration user experience would be nicer with this.
As a Moonlander owner who loves it, it's worth pointing out that most QMK-based boards (including the Moonlander itself with a third party firmware) can support the VIA system for similar easy GUI programming.