The cost of not doing is greater than the cost of doing.

Australian citizens are about to go to the polls to elect a Government. The leader of Labor Party (democrat equivalent) key policy platform is Climate Change. In essence reduce green house gasses in Australia by 45% by 2030 The leader declined to cost this policy. The leader when pressured to identify the cost of reducing green house gasses argues" The cost of not implementing measures out weights the cost of implementation". Discussion then ceases on that subject.
This seems to be deceptive in the presentation.

Is the argument fallacious?

His response falls under avoiding the issue<> and is also a red herring<>. Even though it can be true that the cost of not taking action against climate change is greater in the long term than the cost of taking action to minimize it, the leader puts this statement forward to divert attention from the original question (what are the costs?) and into a different topic (it will cost more to not take action) where he can give a better response and a more appealing answer to the audience.
I also think there could be an equivocation fallacy<> here in the use of the term "cost," as the intended meaning of cost in the question "what are the costs of implementing this policy?" is financial cost, but the intended meaning of cost in the leader's statement "the cost of not implementing the policy is bigger," is future unfavorable consequences.

"The cost of not implementing measures out weights (sic) the cost of implementation".

I don't see a fallacy, but a general claim, opinion or maxim that one would expect s/he could back up
with more than adequate scientific research when pressed.

But if we're adhering to Dr. Bo's guidelines:

1.) It must be an error in reasoning not a factual error. There's no fundamental error in reasoning. It is quite logically sound that inaction in response to climate change could be disastrous and ultimately more costly than the remedy - and not just financially either. This has been vigorously supported by
the science community and economic statistics.

2.) It must be commonly applied to an argument either in the form of the argument or in the interpretation of the argument. The term cost is not ambiguous but has vast implications for both sides. Warmer climate produces more devastating natural disasters, wildfires, and hurricanes, etc. The financial impact of these natural disasters is well into the billions e.g. Puerto Rico, California, etc.

3.) It must be deceptive in that it often fools the average adult. Where's the deception?