Is my dentist ripping me off?!

Sounds like a visit to another dentist for 'evaluational purposes' if it is really needed.
Don't say anything about your other dentist or to your other dentist.
Just go there and say that you might have some cavities and that you want to know for sure.
That might require paying a 'checkup' on your own but at least you'll save a whole lot if it turns out your new dentist is ripping you off.

Good luck

If you like your old dentist go back to him/her. Insurance should not be the primary reason to see someone you don't trust. Ask your old dentist if they are able to file claims with your current insurance carrier and if not then switch to a plan that allows you to see your choice of dentist during your next open enrollment period. I am a dentist and in my experience teachers have some of the best plans out there so if you have a choice in dental plans then get a better one when you can.

Before you agree to undergo any dental procedures with your dentist, go to another dentist and ask for a check up from there. They can tell you if you really have any cavities. You may not feel the cavities, but you can still have them. I suggest asking another dentist.

$100 per cavity.. Oh my.
You should spend the money to fly to Europe, get them done cheaper and still save money of the flights.

Nah being serious, I don't know. They shouldn't rip you off since it's a viable reason to sue so they'd be playing with fire.

Do what others said and visit other dentists to check first.

There are two possibilities. One is yes, the other is that you have very small cavities, and your old dentist didn't feel they needed filling because they might remineralise (it can happen with mild ones). So what you need to do is first, ASK the dentist to show you what the heck they mean. Seriously. Dentists are people, too. So say, "my old dentist said I had none. Can you show me what you're talking about?"

This should get you a demonstration, both with the xrays and with your mouth and a mirror. Don't fill any yet. Ask what's there. If you aren't satisfied with the explanation, get another dentist and lay this out in front of them, tell them that you need a clear opinion here because you've been told two radically different things.

Then, without paying any more yet, speak to the new dentist about a real plan if you do have any. Not "we'll see if there's more," but "okay, here's what's there, and let's not do this/pay for this all at once." You should take care of the most serious first, and then the rest as you can afford them.

You also should be allowed to see and have copies of your xrays. There should not be a 50$ fee on top of the work being done, that seems excessive. So you're right to protest and to question. On the other hand, if you DO have sudden cavities, it might be worth getting a checkup on a six month basis to make sure you don't have some form of illness, that could dry up your saliva.