graci, your question is probably more complicated than you think . . . . The simple answer is that for you, to test whether O2 works for you, you might have to pay around $100 for the whole welding-based setup: a small filled tank, (20 or 40 cu ft -- maybe $40-60?), a regulator (maybe $30-40), and a basic mask (maybe $5-10). If it does work and you want to set up a more optimized system, you'll need at least one larger tank (for home use--you can use the smaller one for portability, in the car for example), maybe a second regulator (so you don't have to use the same one for the big and small tanks), and maybe the better mask that is made for people with CH. All that might add $120-150. Then you will have to bring in the tanks when they need to be refilled, and there is a cost for the refill plus the cost/hassle of trips to the welding supply place.
When you get medical oxygen from a supplier, you typically have some kind of co-pay (others will have to say what that might be; I just don't know and I think it varies quite a lot). Your payments include a regulator and a basic mask. Depending on the supplier, you might get a large tank and a smaller tank, and basic regulators for both. They come to pick up used tanks and replace them. You might want to spend some extra for a more effective regulator (or regulators) and the better mask. How things work out with the supplier seems very dependent on the supplier and the delivery people.
You can read more about welding O2 here: https://clusterbusters.org/forums/topic/5627-notes-about-welding-o2/