Most business schools will publish their average GMAT score, and many schools will also publish a GMAT range, which will probably be the mid 80% range (10% of students are below and 10% of students are above). When researching business schools, “How low can you go?” is not a stupid question. Of course, you want to get the highest score possible. If you are near the lower end of the tail, you will probably need to compensate for this in another part of your application.
A couple of general tips on the GMAT ... First, you should aim to take it only once, but give yourself some time to retake it, in case you do not hit your target score. Second, take a prep course. Most applicants take one, so not taking one will likely put you at a disadvantage. I took two distinct courses (several years apart), and read some material from an additional course, and found that they taught very similar test taking strategies. The key do doing well on the GMAT, I think, is applying the strategies to many, many, many, many, many problems. Did I mention that you should do many problems?