Just a data point here.
I booked GVA-MAN-GVA on January 30, 2024. Flights will be August 22-25, 2024
ET728 Booking Class Q
ET729 Booking Class Q
It's a short flight but I figured, why not try and bid the minimum and check out their A350 biz class seat

YOLO as they say.
So minimum bids were:
ET728 GVA-MAN was $105
ET729 MAN-GVA was $125
Only planning to fly one of the upgrades, IF I'm lucky enough to get both.