Maybe none! A telescope that will work good enough and be easy enough for a young student to use is quite an investment. The $99 telescopes you see in department stores will not function correctly or easily and often just frustrate beginners. Often times it is best to invest in a good pair of binoculars. These can be inexpensive compared to a decent beginner telescope, and can be used for many other activities other than just looking at the sky.
NOT at a department store! The equipment they sell are just toys and will not get you the results you are looking for. When you are first starting out, it is always good to check with and or visit a local astronomy group. They will often have Star Parties where you can go see and look through many different types of telescopes. Amateur astronomers are always interested in telling you about their telescope and what might be best for you. Some local astronomy groups also rent telescopes to club members and could be worth the price of a membership. One local astronomy group that Mr. Chantry is a member of is the Delaware Valley Amateur Astronomer (DVAA). You can learn more about this group at www.DVAA.org
Like most things there is a very wide range. To purchase a beginner telescope, a good mount/tripod (which is actually more important than the telescope), eyepieces, and other equipment I would estimate between $400-$500 dollars to start out. As recommended above, a good pair of binoculars ($150) may be a better option that will help you to see just as much as a beginner telescope and will help you to learn the sky.
These are know as 'Go To Scopes' and are more expensive for starting out. They are very nice, but unfortunately there is a LARGE learning curve to get these to operate correctly. These need to be adjusted and calibrated each time they are set up and if they are not correctly calibrated you will be looking at a whole lot of nothing. A decent beginner scope will give you a chance to learn about how to adjust and operate a telescope and will cut down on the learning curve if you eventually want to upgrade to a 'Go To Scope'.