You can buy split-flap clocks at MoMA [0] for $650. Not cheap. If you want to see a big one in person, the TWA Hotel at JFK Airport in New York has the original split-flap departures display made by Solari di Udine [1] (the same company makes the MoMA clock). Solari also makes other split-flap devices [2]. Not to get off on a tangent, but the TWA Hotel is a very cool place to visit [3]. [0] https://store.moma.org/for…
Split-flap clocks don’t have to be as expensive as the Solari clock. They don’t seem to have the economies of scale to be super-cheap these days, but their mechanisms are fairly simple (essentially analog clocks with really weird-shaped hands) and can be had in the ballpark of $50-$100 if you’re not buying what is essentially a name-brand art piece.
Alphanumeric split-flap displays are way more complex and expensive; you won’t find those anywhere for cheap. The higher-end Solari clocks (the ones with added complications like day and date) likely sit somewhere in the middle; I wouldn’t be surprised if these resemble big watch mechanisms with similar complications.