Ergodox EZ isn’t the cheapest but it’s all setup for you. Hotswap switches too, so you can replace them later if you want to change the feel.

Zsa sells prebuilt keyboards. Kinesics too.

Reddit.com/r/mechmarket often sells diy builds. I bought my dactyl manuform there.

Personally I’d suggest to go moonlander first, as zsa has built really great graphical configurator. Standard qmk graphical configurator is awful and you’ll almost immediately fall into code.

There are many ready-to-go ones in this list: https://github.com/diimdeep/awesome-split-keyboards

Keebmaker make a few of the cooler ones off the shelf (ferris sweep, sofle, corne. I've heard rumours they'll make you a kyria but it's not on their site).

https://keebmaker.com/collections/custom-keyboards

Like just a normal QWERTY split? Kinesis makes a nice one that’s pretty affordable and even has LEDs :)

https://gaming.kinesis-ergo.com/product/freestyle-edge/