https://www.amazon.com/BMW-51-71-2-1.../dp/B004SND71Y
This is authentic hence price tag. Hope it's available.
https://www.turnermotorsport.com/p-3...-rear-spoiler/
This is budget non OEM version made by ECS. From my experience buying splitters made by ECS, the quality is no worse than OEM. Might be worth looking into this one to save some $.
Hope this helps.