You should make sure that you are sitting down when you receive the quote for a harmonic drive of the correct size. However, you can buy pre-owned examples from ebay dealers in South Korea and China. The prices are still significant but still quite a bit less than a new one.
Looks as if a 45 or 50 size drive would be required.
https://www.harmonicdrive.net/produc...-units/shg-2uh
Most of these cnc benders use internal mandrels to stop the tube collapsing. Basing it on a basic Baileigh(?) machine doesn't sound like the greatest idea.