Obviously much more study/testing/research needs to occur, but
given derived o2 levels and amount of time required under therapy, with MD/NP prescribed supervision, an o2 concentrator along with CPAP device might be able to replace the expensive HBO sessions for those with lesser means. Such an arrangement may even prove better/safer. And, FWIW, seems to me to be worth looking into.
breathing high concentrations of oxygen is very dangerous, read up on it.