When you are first considering taking voice or piano lessons the obvious question is how much will it cost. This is a surprisingly difficult question to answer as there are many factors that determine the price of each teacher. This list includes items such as location, education, experience, added opportunities such as recitals and competitions plus many more. I would say if you really want a national average you can expect around paying $15-$30 per half hour. That of course depends entirely on the following factors.
If you are in a rural area lessons will be considerably more affordable. The closer you are to a major city especially one with a highly musical standard such as Los Angeles or New York the more expensive lessons will be. If you live near a major city expect the price to increase dramatically especially for a really good teacher. The best teachers can easily charge $500-$1000 for just one lesson.
Education is also a determining factor in how much lessons are. You can find teachers who are in college or even high school which will gladly teach for next to nothing. However always keep in mind that you get what you pay for and it may not be worth the $5 per half hour if the teacher does more damage than good.
Experience is another big one. A teacher who has had professional performing experience or is well connected in the music industry is going to charge a lot more because they have so much more to offer. If you are considering music as a career this added expense can be well worth it. You are not so much paying for an education as you are paying to have an in into the industry.
Some teachers may seem to charge a great deal but in the long run end up being more affordable than others because they offer more. Many teachers do not make their student but their own books or teaching materials which can make them less expensive than a voice or piano teacher who has lower rates but requires students to get their own books. Other teachers have recitals or competitions which may make their rates more worth it as well.
When selecting a teacher ask a lot of questions. You can ask why they are qualified to charge their rates but also ask about purchasing materials, recitals, sibling discounts, trial lessons, their musical background and anything else you can think of. The more you know the more informed your final decision will be.