This is something that is beyond my knowledge, however I believe that to appeal a matter that has already been appealed you need leave to take it to the high court, it is not automatic that you'll get this.
You need the advice of a good solicitor on this, you may be throwing good money after bad to proceed.
Others may be in a position to reply to you about this.
As Citizen-Joe mentioned above, get some decent qualified advice before spending more money. I don't believe the High Court is actually in play yet. If this was a FWC issue, did you appeal to the Federal Court? The Fair Work Act is a Federal statute, which to me suggests the Federal Court would have jurisdiction to hear an appeal over an FWC decision. If you've been to the Federal Court and been knocked back, I believe you're entitled to seek leave (not automatically granted) to appeal to the Full Court. My understanding, which I must qualify by pointing out that I may be wrong, is that an appeal to the Full Court is effectively the Federal Court sitting as the Court of Appeal. The High Court won't give you the time of day unless you have exhausted your opportunities in the Federal Court. To the substance of your question, you're going to be appealing your latest outcome. Your appeal will need to show how the Court erred in confirming the the FWC decision. If you can establish that, they may send you back down to the level of the Federal Court with a direction to re-hear your original appeal giving weight to the reasons it was deemed wrong, they may throw out the FWC decision, or they may force the FWC to re-examine the issue - they'll have a number of potential outcomes open to them, including denying leave to appeal or throwing out the appeal itself. There is only one certainty - much time, stress, and expense. Make sure it's really worth it, and then make sure you get damn decent legal advice before rushing in to anything