I was also told I have Fibrocystic breast disease many years ago. I am 42 and started getting mammograms about three years ago. On my third mammogram, I was asked to return for a follow-up because they saw something they weren't sure of. From there, they sent me for an ultrasound where they decided what they thought they had seen was not a problem. However, on ultrasound, they spotted a small 5 mm density which had not been detected on the mammogram. From there, I was sent fora biopsy which came back positive.
I don't know the cost of ultrasounds, but it might be worth inquiring if they could check you out with that instead of an expensive MRI.