I have one of the crappiest private insurance plans available, and they still pay for my GP visits and one of my HRT-related meds, finasteride. They don't pay for the estradiol obv but it's so cheap anyways.
They pay for the labwork and visits 100% minus 30 dollar copay, which is really surprising given the fact that in every other area they cover little to nothing. (talking 250 dollar ER copays and only paying out like 30% for specialist visits)
I'm fortunate enough to not have to go to an endo to get my levels checked, my GP does it all there.
I just don't think the ins company knows that's all for HRT/transitioning. I would hope any problems that stem from HRT (hopefully none) they would pay for, and when the affordable care act comes into full effect I hopefully won't have to worry about it anymore.