My nearly 7 year old DD was diagnosed with ankylosis when she was 5.
During a routine visit, our dentist noticed that her second back molar had not erupted fully and he sent her for X-rays which confirmed ankylosis. She was referred to an orthodontist for treatment. The treatment option that we have been given is that they remove the problem tooth and then place a bracket around the back molar (the one behind the extracted tooth) and a bracket around the molar on the other side of her jaw and run a wire between the two brackets which will sit in behind her teeth. This will then hold the back molar in place and prevent it from moving forward into the space created by the extracted tooth. The brackets will need to stay in place until the new adult molar erupts into its proper space.
We haven't actually commenced treatment yet as the orthodontist has been waiting for her back molar to have erupted enough to be able to get a bracket around it. In December he decided it was time to go ahead, so sometime in the next month or so we will be getting the extraction done. The orthodontist won't do the extraction as he said it will need to be done under a GA so we have to go back to our normal dentist for a referral to someone else to do the extraction

I don't know yet what type of specialist will do this. Once the extraction is done, then we go back to the orthodontist for the brackets to be made up and fitted.
As for cost, so far I have only paid $100 to the ortho and the X-rays have all been bulk billed. I have no estimate of what it is eventually going to cost. We have PHI, so I am hoping some will be covered.
I am not looking forward to DD going under GA but I figure it will be far less traumatic to have a tooth removed this way - the ortho said it will be a difficult extraction.
Best of luck to your DD