Student or Learner
When someone answer "Not if we can help it". What does it mean?
It means that they will do what they can to stop the thing from happening. (Going over budget, in this case.)
Quacam, please note that the context should have been given in post #1 - not #3.
"help it" - 'help' is used strangely, almost opposite to its normal meaning, in this very useful idiom.
"I can't help it" means "I can't prevent [myself from doing] it."
A: "Why did you drive into the river?"
B: "I couldn't help it. Someone removed the warning sign!"
A: Stop crying! It's not that bad.
B: I can't help it! (I can't stop crying)