on A/C (from what i know/seen):
- if flight is overbooked and the "flight manager" see the "need", you will be upgraded from Y to C or C to F for free
- Money Upgrades from Y to C or C to F based on availblity, i know its 500$
from TLV/NYC, On last flight they asked only 250$
- Money Upgrade on A/C can be paid with points (1pt = 1$) rather money.

I have also seen flights where since few business passangers where on a/c,
they were move to F (no one on F/or no F), And all TPL/PL/GL/"Friend Of..."
where placed in Business (with Y class meals...)
Seen this 3 times already...

Thanks,
Eran.