So my R50 is at about 150k miles. I'm thinking it's time to replace those as another tranny rebuild is in the very near future. I've seen some with a 75k mile warranty, for quite cheap versus the more expensive options ($400 and up).

What would you guys recommend?

 

GKN OEM supplier axles HERE are a sufficient and less costly replacement vs their Genuine counterpoints. In stock ready to ship. They also have a 24 month/24,000 mile warranty. I would stay away from aftermarket axles as they're usually not manufactured well and you'll have issues sooner than later. Let me know if you have any questions.