I'm finally going to buy a bike next month. And a helmet. I'm wondering how much I should budget for buying a helmet.
I'll be riding around New York City, so I want good visibility around me. And safety is a big concern for me as well.
Testing of helmets shows that there is little difference in impact protection. A better quality helmet, defined in this case as one that fits your head, is well ventilated, and looks good.
A well ventilated helmet prevents you from overheating while riding, especially at high speeds. A helmet that fits stays put on your head during a crash. And one that is comfortable and lightweight is less noticeable while you ride.
From a pure safety standpoint, buy a DOT/ANSI certified helmet, and you'll be fine. If you want to enjoy riding, and not mind wearing the helmet, be willing to spend more. $300 dollars is not out of line for a really high quality helmet, but that doesn't mean you need to spend that.
Find one that fits, ask your LBS to explain the ventilation differences between it and its more expensive cousins, and find one that fits in your budget. Looks good can be important, too, but that's personal and subjective.
The Bicycle Helmet Safety Institute submitted samples of six helmet models to a leading U.S. test lab: three in the $150+ range and three under $20. The impact test results were virtually identical. There were very few differences in performance among the helmets. Our conclusion: when you pay more for a helmet you may get an easier fit, more vents and snazzier graphics. But the basic impact protection of the cheap helmets we tested equaled the expensive ones.
The results are a testimony to the effectiveness of our legally-required CPSC helmet standard. Although our sample was small, the testing indicates that the consumer can shop for a bicycle helmet in the US market without undue concern about the impact performance of the various models on sale, whatever the price level. The most important advice is to find a helmet that fits you well so that it will be positioned correctly when you hit. We have a page up with details of the testing.
In many countries all helmets legally sold meet a certain minimum standard. So there is no "too cheap" option, as the cheapest helmet you can buy will be considered safe enough. In this case spending more gets you a lighter, better looking (subjectively) and more comfortable helmet.
The USA also has a mandatory standard. For information about the standards and also plenty of other information and studies about the safety benefits of wearing helmets, see this wikipedia article
The American National Standards Institute (ANSI) created a standard called ANSI Z80.4 in 1984. Later, the United States Consumer Product Safety Commission (CPSC) created its own mandatory standard for all bicycle helmets sold in the United States, which took effect in March 1999.
Although safety is a big concern, I don't think that a helmet per se will keep you safe. Wearing a helmet may make the difference between being lucky versus unlucky, if you're in an accident. I wear a helmet (well, a hard hat): I'm not against helmets; but the other things you do, e.g. choosing where and how and when to ride, would probably have a bigger effect on your safety.
I don't know that any helmet would impair visibility: it moves when your head does (and, I expect, stays up on the crown of your head instead of slipping in front of your eyes).
I may be wrong but I think that what you're buying with a more expensive helmet would be:
I bought a "Bern Brighton" hard hat because it was cheap and comfortable and (I hoped) more likely to at least stay on, in an accident, than others in the store which fit less well.
Edit: Someone mentioned that some helmets come with visors, which can interfere with your visibility when you're in a "heads down" position. Now I recall, I did notice some with a visor, often a detachable visor, and reflexively (note that I'm a novice buyer/user, not an expert/salesman) avoided them: I reckoned that instead of a visor I could wear sunglasses instead, if it came to that.
A more direct answer: If you shop in a bike shop you'll probably have to shell out $50-75 for something that fits and suits your taste. If you shop in a discount store you can likely find a serviceable helmet for $20-30, though it may not be vented as well, if that's a criterion for you.
Main criteria would be