As a former dental assistant, there can be situations like yours, but not real common. I would continue with your plan of a second opinion. You'll need the x-rays to take with you, so just request a copy. (This can easily be done!) The dentist should be able to show you each of the areas on the x-ray or in your mouth.
As far as the cost...the type of filling material used may make a big difference in the cost.
Hope you get a satisfactory resolution to your situation!