Every school handles its applicant pool differently, and most don't share their exact methods, so it's very hard to say with certainty what, if any, factor will automatically flag your application as unacceptable for a given school. A school might use any of a range of arbitrary factors to shrink a large applicant pool, including GPA, GRE or other standardized test scores, the reputation of your undergraduate institution, etc. Prospective grad students are understandably desirous of being able to make definite statements about what will or will not get you into a given college, or grad school in general, but the reality is that the specifics of the application consideration process are a black box to us.
If you are concerned about wasting money and effort, then here is my advice: Draw up a list of schools that you know you want to go to. Check their entrance requirements to see that you meet their minimum numerical requirements (GPA, GRE, etc.) Cross off any schools whose stated requirements you can't meet. Then apply to the remaining schools. Unless they say outright they won't consider someone under a specific GPA threshold, then you have a shot, and that's the best assurance you are going to get.