Where does haute horology begin?

[dexvd]

So by definition, horology includes any complication beyond a two hander whereas haute horology is watchmaking in its highest form, with the emphasis on the movement technology rather than the case (cartier for example), bracelet (AP for example) or dial (Lange 1 for example).

I have been interested in watches and collecting them mainly based on their design but am becoming more interested in the idea of haute horology and movements that are really pushing the limits. The ultra thin movement race interests me but in terms of complication or extreme movement technology is something like the JLC MUT perpetual calendar the entry point?

What other interesting movement technology and complication is out there that is attainable pre-owned for under $20k? What do you consider counting as haute horology rather than watch design (interesting case, dial, etc).