It's the same with train tickets in Europe!

I live in Budapest and regularly have to go to Wien. If you buy the ticket from the hungarian railways it costs the half or less than compared to the austrian railways.

Example: next monday

Hungarian BP>Wien https://i.imgur.com/9rZgB8c.png

Austrian BP>Wien https://i.imgur.com/mn95IrV.png

Hungarian Wien>BP https://i.imgur.com/GymMOaW.png

Austrian Wien>BP https://i.imgur.com/zN3VCDv.png

I always tell my friends coming from Germany or Austria to buy tickets from the hungarian railways because it's much cheaper.