Hello MM Jack, my thoughts are with you and feel the sorrow for the situation you are in as it's not a position anyone would want to be in.
I'm definitely so sorry to hear about your father's condition and it certainly puts you in a very difficult situation, perhaps if I can make a couple of suggestions, and please these are only to try and help you in any way possible.
Are you able to contact him via skype, zoom or duo and these are the only ways that are free to talk and view each other, so I'm not promoting anything that requires any money at all and can be done via computer or mobile phone.
Compassionate and bereavement leave is a possibility, and you may be able to get a credit card to pay for the trip, I know it puts you in a difficult situation as you still have bills to pay, but try and contact him through family/friends via one of these media contacts, at least you can talk with him, I'm sure he will understand what position you're in.
If I was the father in your position I would certainly understand how difficult it may be to travel o/s to visit me, and I mean no harm in saying this.
I hope this may help you, but very sorry for you to be in this position.