I can’t help with costs these will be regional, but my thoughts are
How much use will the study/office get? Is it better to keep greater separation from the lounge if you’re going to be wfh regularly?
Where will the gf wc go, if you remove the on suite, the lounge becomes an odd shape, if you remove the existing wc and convert the on suite you have access directly from the lounge and some excess space (Addison also storage?)
If it were me cost dependant I’d consider knocking the study through into on suite, turn the box part of existing study into the wc, perhaps take some more of the study to Mack coat/shoe storage.
Lose all the existing bedroom walls, and the wall between kitchen and that area and put bifolds between kitchen and current lounge.
Have a play with
https://floorplanner.com/ a basic account is foc and should help visualise any changes