Might not be appropriate here but by way of comparison - Emirates sporadically offer me Economy to Business Class on the DXB -LHR or LHR - DXB route. They charge $600 USD one way and it's offered when you go to web check in (although I have sometimes received specials at $480 USD one way via email 5-7 days before departure). You don't get lounge access or pick up with these but it is basically a double upgrade from a BA point of view as EK don't have WTP in between.
FYI, I never buy these as flight is only 6-7 hours long and EK is just fine in Eco for this length of time.