Depending where the manhole locate, My guess will be around 15-20k range. You need to dig the floor for proper pipe relocation.

I don't know what the cost now. 40-50k sound high. Oh btw you need to get approval from local council too.

architecture drawing

And all these also cost monies

Any structure change yes. And people usually ignore it because is internal. But once neighbor complain, all work will be stop, and will be fine than apply permit.

If you plan to do other renovation the toilet relocation maybe cheaper. Also take note of the permit and process these also need monies.