EBay has lunch box sized oxygen concentrators -- coming from China -- for about $350 including shipping. I just bought one
($335) to use overnight. I really need to talk to my doctor and get a professional US unit from insurance, but in the
meanwhile I thought I'd see if this would help. (Solution for me will probably be a CPAP with an oxygen concentrator added,
at night only.)
Anyway, the unit is the size of a lunch box -- about 4" x 10 x 8 (from memory and guessing). I have no idea of the quality
of these units, or the lifetime one can expect. They run on A/C and/or battery, and they include a car charger too. Settings
include 15 minutes, 30 minutes, or 8 hrs.
Here's a sample ebay listing
ebay clicky
I tested mine with an O2 meter from my workplace. I cannot verify the "29% oxygen" claim, since my meter is only looking
for "too low for life" -- but it did peg out the meter at 22%, which is higher than normal. So it is producing something more
than straight air.
You might at least be able to tell you doctor that they do exist, in a small size. If, that is, a concentrator is able to supply enough
oxygen for you.