At the time of Broly - The Legendary Super Saiyan, Broly's power level was One Billion, Four Hundred Million. It was confirmed with a V-Jump scan.
Man, do I hate how they treated Broly in the movie. I understand they had to kill him because of plot and movie purposes, but DBZ haters really try to downplay the
second most powerful character in all of DBZ/GT by using his death as an excuse . Super Saiyan 4 Gogeta had a power level of One Billion, Five Hundred Million. Broly is barely under him.
Scratch that. My sources were unconfirmed. I have confirmed sources now on power levels. Yeah, he's definitely not as strong as that. He is weaker than Super Saiyan Gogeta. He wouldn't be Super Saiyan 4 level. V-Jump shows Super Saiyan Gogeta's power level at being Two Billion, Five Hundred Million.
Broly (and as you can see, Cooler's power level was 470 Million)