You're not alone. These commonly fail around 60-70K mark. My dealer quoted me $1k to replace one side, which needless to say is ridiculous. My breakdown was $450 for the part, labor, and alignment.
The thing is, the original part is made by Lemforder which you can buy from FCP Euro for $125. It's the same identical part since Lemforder is the OE supplier for BMW. If you're handy with cars, it's on the medium difficultly scale. Took me about 1.5 hrs each side for a total cost of $300 (with some additional BMW nuts and bolts). If you can find an indy shop that uses Lemforder instead of BMW stamped Lemforder parts, it should's cost you more than $800 for both sides to have them do it for you.
I'm not sure why the alignment is honestly needed - the thrust arm doesn't have much impact on wheel alignment.
https://www.fcpeuro.com/products/bmw...rm-31126777733
https://www.fcpeuro.com/products/bmw...rm-31126777734