I've never been offered a buy-up. Ever. I admit, I am often either upgraded or pending upgrade, but it hasn't always been that way.

Recently I was flying Norfolk to Honolulu with 3 colleagues. 2 were GMs 1 of whom had purchased E+ for the year and 1 was 1P. I'm 1K. The GM was offered a buy up to E+ ($85). The GM with E+ was offered a buy up to F (more, but I don't remember). The 2P was offered the exact same buy up to F (these 3 were all going to San Diego). I was offered nothing, but had a ORD to HNL CR1 pending.

I've never seen buy ups offered when I had a SWU or CR1 pending, but have when I was trying to use E500s.

So I conclude (with no more evidence than the above and old threads here) that buy ups come after miles / SWUs/ CR1s and before the B list. Anyone have refuting stories?