Answer:
There are two standard types used in modern day bands: the most common version plays down to the E-flat below the staff, you need a bass peg to hold it up high enough to play. This kind is the more affordable kind and is good for middle school students and most high school students.
The second kind has what is called a "Low C extension", it can play down to the "C" two octaves below the staff. This Bass is longer and only requires a short peg (or when the player's torso is short enough, no peg). This Bass has more keys (meaning more delicate) and can be more expensive to maintain. Most Low-C Basses are built for high end performance, they are good for top band high school players, college players, and professionals. This type of bass has more agility and has a better tone on average, but some companies are making budget extended bases and they are not very good.
If you want to get your own bass it's important to know how far you want to go with it. If you just want to play for fun then stick with a high end standard bass that goes to E-flat. If you want to go to college and be a pro, get a high end Low-C extension.
(interesting fact: in the early 20th century Bass Clarinets were also made in the key of A, while it's still possible to get them, they have fallen out of use in bands/orchestras)