Your head will get hot in a cheap helmet if you are working hard. More expensive helmets are usually more adjustable, and cooler. If you find a helmet that fits, and keeps you cool you are more likely to wear it.
After years of trying different helmets from loads of different manufacturers, feeling uncomfortable, and thus going out without one, I've finally found one that fits properly. For me the Specialized Decibel is worth the extra money, because I can put it on at the start of a ride, and forget its there!