Looking to buy a new one.
Why are the prices so far apart? $48 to $250.

 

For the exact same pump from the same vendor?
You could check options from another source such as Rock Auto -
2019 JAGUAR XJ 5.0L V8 Supercharged Water Pump | RockAuto

But my experiences with my 2012 AJ133s in my Range Rover and the XJ, I've found that my best bet for their cooling pumps have been genuine JLR pumps.
To me, I've found it's worth the price difference - again, to me personally.

 

No that's from several different vendors. I don't understand how the same part can range so far in prices.

 

Post what part number your looking at.
I agree with Mark. I recommend and use JLR water pumps. Now are there good after market ones? Probably but since I know Jaguar has released at least 6 prior versions of the water pump they apparently had a LOT of problems!

My 2014 XJR bears this out as I lost my OEM WP at 28K miles. Replaced with the latest version part number ending in 3909 under factory warranty 7 years ago and no problems since.

While your in there don't forget all the crappy plastic cooling parts you can finally replace!
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The are a few manufacturers of aftermarket part, that like Clubairth1 said may have some decent products, but the only certain quality parts are the genuine JLR product.
OEM does not mean it's a genuine JLR pump either. It should mean it's from the same manufacturer that supplies them to JLR, but that's not true because most vendors will claim they're from the same production line when they're not just to sell them.
I've removed failed pumps from Uro and from GMB that didn't last as long as a pump should - but like Clubairth1, the best results I've seen is from the genuine JLR pumps with the JLR markings on the casting. New of course, not used.
Money can be saved on some aftermarket items that aren't critical parts, but for the important stuff, I'll pretty much always suggest using genuine components.

 

I've had good luck with Gates waterpumps on all of my other vehicles. So I would trust them and oem.