First off: I'm not a professional photog, and have never been paid for my photography.
I suspect there are many things in the photography industry that you don't yet understand. A couple of things, in my unprofessional opinion:
- Having a good camera doesn't make a good photo. There are many other factors at play, which I don't want to elaborate here on. The internet is full of info.
- Under charging for work is bad on the whole industry. That being said, if you are only using your "higher end camera", a kit lens, no strobes or other lighting equipment, no portrait techniques, etc, then charging 100-200 compared to 600 might not be under charging. If students want mediocre quality shots for a greatly discounted rate (compared to the 600), then that's what they will get what they pay for, or less. If your shots don't turn out great, they will not buy them.
If I'm wrong and you are well equipped (good portrait lens, lighting, backdrop, etc), then you might be successful if you know what you're doing.
Just don't expect to be able to have people pay hundreds of dollars for pictures just because you have a "higher end camera". The clients could care less about what camera was used. They will only care about the final product.
Any more experienced photogs out there, please correct me if I am wrong.