Thanks for the replies!
- I only found 12 speed Leonardi cassettes. In the 12 speed range, there are good options from ZTTO.
- Ekar would be great, also price-wise (although apparently just 9-42 or 10-44). However, it's a bit more difficult to find good and cheap wheels with campanolo freehub body...
For context: a 9-46 13-speed cassette would allow for a great 1-by drivetrain for road bikes in hilly terrain based on the wheeltop GeX (for instance with a 44 chain ring in the front).