1968 Dart sudden rear end noise.

An a body 8.75 differential is typically a fairly expensive piece when you find them. I sold a bare housing last year for $500.00. I've seen them for sale here on FABO for anywhere between $750.00 to $2500.00, depending on the condition.
Wow. So what is my best option here? Is the 8.25 much sturdier? I just don't understand why Chrysler wouldn't just put a more robust rear end behind all the a bodies.
I like the B body cars like.the Satellite and Coronet a lot too. So all 8.25 dart rear ends had larger bolt pattern wheels? What would I expect to pay for a 8.25 rear?
P.S. My dog makes that same face all the time and rests her chin on me like that.