Almost certainly not. There's a lot of engineering behind helmet design and I would assume that the more expensive ones are scrutinized more thoroughly with regards to aerodynamics, venting/cooling, etc. And just because they might have less material doesn't necessarily mean they are cheaper to make either. They could use a different (e.g. stronger) material to give it the same mechanical properties as a cheaper one would with less material removed so that it lives up to the same safety standards. The extra holes could add complexity to the molds as well which may lead to increased cost (albeit marginal).