'72 280 SE 4.5 Transmission Swap?

My 1972 SE 280 4.5 Gas powered V8 is having some transmission issues. The mechanics are having a hard time sourcing parts so far and quoting me between $2,500 and $5,000 to rebuild. I'm wondering if there's a transmission swap I could do with a different model/make that would be less expensive.

Or, is there a parts supplier to provide more reasonably priced parts for the 72 transmission.

I searched the forums, but did not see a topic specific to transmission swaps.

Thanks
Charlie