Things to consider when you are looking for an instrument:
Renting vs. purchasing:
When renting an instrument you get the luck of the draw from the music store's stock. You rarely get to select the instrument you want and can sometimes end up with one of poor quality.
After about three years of renting, you could have purchased a very nice instrument for what you paid for the rentals.
If you decide to rent, get to the store as soon as possible in order to get the best instrument.
If you are afraid to spend the money to purchase a good quality instrument because you fear your child might stop playing, consider this:
Your child is more likely to have success and enjoy playing on a better instrument.
Quality instruments maintain their value. If you purchase a quality instrument and your child stops playing, you will be able to resell the instrument. The difference in price between what you buy and sell it for will be close to what you would have spent on renting, but you've had a good instrument all the while and given your child a better opportunity to succeed in music.
If you have decided to purchase an instrument there are many things to consider and weigh. It is a very good idea to discuss it with a music teacher (or two). They are usually very happy to help.
See the page on "your instrument" for some recommended makes and models
Think of shopping for an instrument like shopping for a car. Here are some things to keep in mind.
Figure out what your budget is and then compare your options in that price range.
Don't buy a lemon!! There are some very nice looking instruments with attractive prices that will cause your child a lot of aggravation and you a lot of trips to the repair shop. There are no quality brand new instruments for under $300.
The brand name is important. Ask a qualified music teacher to guide you toward the respected brand names for the type of instrument you are looking for.
Each manufacturer has many options in their line of products. For middle school students, I recommend a good quality intermediate level to professional instrument.
A used instrument can be an excellent option. Quality instruments, that are not mistreated, stay great for a very long time (My own instrument is close to 50 years old).
Go take some instruments for a test drive. There are several local music stores that carry some good (and not so good) instruments both new and used.. Your child will quickly be able to tell which instruments play well and which don't.
There are some online instrument dealers that offer competitive prices (without tax, if they are out of state) and the convenience of online shopping. You just don't get to try before you buy.
I have had a number of students find success on E-Bay. But, you have to do your research first so that you really know what you are looking for.