You can get oxygen prescribed by a competent doctor (which means maybe there's a 30% chance of getting it, maybe up to 60 or 70 percent if you provide them with the info and you're persistent). Lots of people get welding oxygen from a welding supply store and order a mask and regulator over the internet. Initial cost might be $200-$300, depending on a lot of factors (size of tank(s); quality of mask; rent or buy tanks; local market); only cost after that is tank refills. If you want specifics, just ask.