2012 Chevrolet Cruze - is an intake manifold diaphragm pricey to fix?

Is a rupture in the intake manifold diaphragm common and expensive to repair?

Common , doubtful but that does not really matter. You have one and it needs to be fixed. As for cost call for estimates because we don’t know where you are or who you might use. Also the shop will want to verify that is the actual problem.