Looks like you have been doing some pretty good analysis but...

Looks like you have been doing some pretty good analysis but there are a few things that you are getting wrong while doing these comparisons.

TAW have their price locked for 2 of the 3 years of the starter pit at USD$880. Therefore doing their PFS on these numbers isn't unrealistic. Doing a 20-30 yr DFS at those numbers might be.

The $500 opex figure is in AUD. Use the same currency and you will figure out they have pretty good margins.

Because TAW have done their feasibility study on a small starter pit their opex numbers are more accurate than everyone elses and actually give a realistic representation. GXY are almost a year on from commissioning and they are still producing at a cost of ~ USD$370. That works out to be roughly $500.

Companies using a PFS/DFS over 10+ years get a much better average because the costs in the middle years in particular will be so much lower while early and late years a bit more expensive to dig out.

BGS have the advantage that being at surface their strip ratio will be low and overall their average opex might be a bit closer to what is experienced in reality early on.

I find it highly unlikely a buyout would be for the NPV of a project, that leaves all the execution risk on the buyer. No-one will pay that kind of premium.