Hi,
When vias to planes are cosidered, whether it is power or ground, I've noticed that general tendency goes towards increasing the quantity of vias rather then their size. If I am not mistaken, geometrical calculation will support this decision.
How many holes does cost. How many drill sizes cost. If you can keep all the VIAs the same size that helps the board house.
In small volumes I have never seen a charge, but I know in large volumes everything is added up.