I have done a key post on the issue of appealing an FSO decision.
Appealing an Ombudsman's decision to the High Court
In summary - unless the Ombudsman's decision is bizarre, The High Court is not going to interfere with it.
I don't know the fees but I would say that you should budget for €50k for yourself and €50k for the FSO's fees if you lose, as you are likely to do.
Are you allowed to roughly explain what your experience was ? I dont understand why this process is so secretive , surely we can all learn !!!!!!! and share info