I'm in Beaufort, SC - between Hilton Head and Charleston, SC. I'm getting oxygen from Resource Medical Supply Group https://resourcemedicalgroup.com/ who have multiple locations in SC and one in Savannah GA. By paying out-of-pocket, its $10 per E (M24) tank (680L), and they just got me an M122 tank (3455L) for $25. So the bigger tank is quite a bit less. I haven't finished my cycle so I'm not sure how much I will be spending. As long as they can keep my on the larger tank for most needs, I think it will be pretty reasonable. By comparison, they told me it would be $100/month for oxygen delivery service if it were covered by insurance. The store is only 3 miles from my house, so the proximity makes it very easy to get to for me. My focus right now is to make sure I can get sufficient oxygen from a steady supplier. They only had a 8L regulator for the large tank, so I will order one of my own.
So I'm trying to get both sizes of tanks, and 25L regulators for both sizes.