just a reference point...
colleague flew IAD -> CDG last week, he paid €1500 for a return (CDG <-> IAD) Y ticket..I do not know the fare class, but he bought it only a week or two before departure.
Upgrade costs...all Y -> J
CDG -> IAD
Miles - 70k
Money - €500
IAD -> CDG
Miles - 90k
Money - €600
The exact costs may be slightly different but it's pretty darn close... I cannot comment on how full the cabins were. Either way, I remember us discussing that the cash cost is not too bad but the miles cost is absurd.