On a round trip ticket this April/May:

GRU-CPT: range began at USD 300
CPT-GRU: range began at USD 500

About 7 hours before flight departure time from GRU, the last 4 seats in business ceased to be available for sale.

I've not yet heard of my upgrade bid was accepted or not. But can't log into to upgrade site to check; will find out at the airport.

UPDATE: The system seems fatally broken. Despite an e-mail confirmation received at the time I made my bid, check-in agent tells me there is no record of me (or anyone else) on the upgrade list at the airport.

There were still upgrades for sale - at the laughable price of USD 2500 per seat (higher even than the maximum allowable bid, which I think was USD 1500).

As I waited to check in at the airport to not risk inadvertently canceling the upgrade request, I'm now stuck in an undesirable seat way in the back of economy, with no way to have my bid processed, and at least 3 empty seats now in the business cabin.

I'm surprised, but not delighted.