The biggest problem is getting a bow that fits you. Do you know your draw length? Do you know how that translates to all the manufacturers' draw length measurements, because they are all slightly different? None of the major manufacturers put out junk, or they wouldn't be in business very long. Not like the gun business....
Shoot a few and pick the one with the draw cycle and shot that feels best to you.
When you buy from a shop (pro shops are DEFINITELY preferred, as the big box stores simply do not normally have the resources to work with you through the whole process), they have the means to swap cams and set up the bow to fit you. You may get lucky and buy a used bow that fits perfectly, but don't go through months of frustration attempting to shoot a bow accurately that doesn't quite fit, and develop bad habits in the process that you will have to later shake. I speak from experience, and would have been much better off spending the money up front for a proper bow fitting.
This is important because it directly impacts your ability to hold groups with broadheads. You may be the best field point shooter in the world, but those groups make no difference in the woods. Any form issue you have will be magnified with BHs.
Now accessories, THAT's where to save money on used equipment! Sight, rest, quiver, stabilizer, release, etc will add up quick. Buy these used and bring them to the shop...just don't buy crap.
Another tip, one does not simply "get into" bowhunting...you have to completely immerse yourself in it to be routinely successful. I learned a hell of a lot more about hunting deer in the couple years it took me to finally tag one with my bow than I did in 15 years of rifle hunting! It's definitely addicting (frustrating)!