The most common and most likely answer to this crossword clue is the 4 plus 1 plus 4 letter word COST A BOMB
I've seen this crossword clue in The Times
C
O
S
T
A
B
O
M
B
More clues leading to the result COST A BOMB
Buddy explains!
The straight part
We know that "As bill passed on involving millions, this certainly ....?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case as bill passed on involving millions, this certainly ....? = cost a bomb.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.