My last two helmets have been from Lidl and cost less than a tenner. They are ok but somewhat over warm for a sweaty chap like me.
What I found to be a useful exercise was going to the Specialized Concept shop. They have a display of all the helmets in their range. I compared weights with my current hat. The cheap ones were the same or heavier. The mid range ones were about the same, they might be lighter but not noticeably so. The top of the range ones were much lighter, definite improvement.
Apparently the more expensive ones also have better air flow and so are cooler in the summer.
I would assume that this pattern of helmet models is pretty much the same for all manufacturers
What I found to be a useful exercise was going to the Specialized Concept shop. They have a display of all the helmets in their range. I compared weights with my current hat. The cheap ones were the same or heavier. The mid range ones were about the same, they might be lighter but not noticeably so. The top of the range ones were much lighter, definite improvement.
Apparently the more expensive ones also have better air flow and so are cooler in the summer.
I would assume that this pattern of helmet models is pretty much the same for all manufacturers