They are worth more than you think, as you probably don't know, you cannot buy the original s54 pump spuriously as the manufacturer of the pump is first of all unknown and second of all not available outside of BMW.
By all means you can source a TRW, VALEO, INA, GATES, MARELI, SKF but I don't think any of them have the same sort of reliability as the original s54 pump. It's a Motorsport pump in fairness.
It's a rare occurrence when an s54 water pump fails and usually 130k miles or more. Can't say that for alot of the other models.
S50 pumps are about 400 euro from main dealer. I wouldn't buy a spurious pump for that engine either.
Must actually check and see if this pump would fit my s50!.