select your column
then choose edit / goto and click the Special button
choose blanks
click Ok
type 0.00 and press control & enter
this should put it into every selected cell - if the formatting is not
correct, change the formatting before you click on another cell to unselect
the range.
If they are truly blanks you can use the following, select the whole range,
press F5, select special and check Blanks, press enter. Type 0 and press ctrl
+ enter
format as 0.00