One suggestion would be to tie in how this would benefit them financially (how much your treatment is costing them right now and in the future, also tying in cost for mental health services as related to this condition if it applies for you), and how HBOT can actually save them money.

I am sorry you have had to go through so much, and that it has spread for you. I am currently going through HBOT--I have had about 23 treatments now and plan to do 40. I feel like it is making a difference (although it took awhile to get results--you need to be patient). The other woman I am getting treatments with was pain free after about 15 sessions. I am excited to get back in the chamber on Tuesday. If this turns out to be the key treatment for me, I'll also be consulting with insurance to cover maintenance sessions. I had med pay from my accident that covered most of the 40 sessions I'm doing now. Best of luck to you!!