HMO's are often flakey when it comes to covering benzos like xanax. Some do it but lots don't. If your present insurance covers regular alprazolam it will cover the extended release as well. There will be no difference in coverage. I spent years in that industry.
I can only imagine that you have a really tough time finding drs that really understand post polio. It's been a long time since it was a real problem in this country. I doubt many people even know anyone who had has polio unless they are my age or close to it. One of my oldest friends had polio when we were kids. He has struggled with the same things you describe for a long time.
Hope it all works out for you. Keep us posted. God bless.
I am not a dr. My statements are based on years of experience and related education. Consult with the professional of your choice regarding matters of concern.