The ATR25 is simply too short to be very useful as a boom mounted shotgun mic.
The longer the mic is, the more directional is it, this is important, especially if you are shooting a wider shot, so the boom can be out of the shot, but the mic will still pick up the dialog.
These mics aren't really ideally suited to boom use though. Ideally you would want to use a mic with an XLR connection, as it is a balanced signal that is sent through the cable, vs these which are unbalanced. The benefit to a balanced signal is that it will reject a lot of electronic interference that can otherwise be picked up. The last thing you want is your boom to act as a radio antenna..
I'm not sure where you're located in MN, but there are some good rental options available here that might be worthwhile for you to utilize until you make a decision what to purchase.
The perfect set up would be a beachtek adapter, or other XLR adapter, for your camera, and a good high quality shotgun mic. Sennheiser ME66 or 618 are kind of the "industry standard" though there are other decent more affordable options (those mics are $300 or more, though worth every cent)
To be honest, the title of this thread scares me... Audio is a very important part of your final product, and if you buy a dirt cheap mic, you're going to end up more often than not with dirt cheap sounding audio..
The equation really doesn't make sense, if you spent several hundred dollars on a camera that will take great images, why would you couple it with a $50 microphone? Especially when audio accounts for as much as 70% of the viewing experience of the final piece... that's a question I've been trying to figure out for a while.
