Regardless of the microphone you will use, most likely you won't like the sound quality that your D7100 will record. I have a D610, and the buzzing sound was horrible due to low quality preamps in the camera. You can watch a video here :
https://vimeo.com/85673816 showing you the problem.
For that reason, and to get XLR connections, I purchased the
Tascam DR-60D PCM linear recorder. But this is only half of the battle, you will still need to hook it up to a decent microphone. I already had some of different types, but if you want good quality at a decent price, the RODE NTG1 or NTG2 (with phantom power) shotguns are great for the money, but you will need a boom pole and the attachment. A lavalier microphone would be the way to go for your specific application, but the good ones are pricey. I use Sennheiser body packs and my transmitter and receiver cost around 800$, maybe not the kind of money you want to spend. Sorry, I can't help more on that end, but just remember the sound on your D7100 will suck if you feed it directly from any type of microphones.
Lastly, another option maybe to get the
Rode VideoMic Pro. The preamps are much better, and you can actually feed your camera by lowering the recording level in the camera, while boosting the signal +20dB coming from the Rode mic. Overall, sound quality will be much better, I would even say acceptable, but you'll be limited in the distance you are from your subject. If you're planning on shooting at many different angles and distances, then your sound will be uneven, a lavalier is the only solution then.
Hope this helps,
Benoit
