I agree with the others that they are expensive, but you only need to buy them once in a long, long time. So, for that reason, they are a great deal---much longer lasting, for example, than going out to a restaurant.
Amazing isn't it, how "expensive" ruler seems that will last you for years but people will spend $5 for a cup of coffee or $20 for a meal (or more) at a restaurant that only lasts for a few hours without complaining or blinking an eye.