Yup, I have a whole bunch of tanks now that run at 300 bar. First was the Benjamin, still use that, acquired a few more smaller ones from guys here and there that are also 300 bar and do fine. But once I started shooting big bore and in particular 457 and 510 caliber, those little tanks just didn't cut it. So a while back I did the Ebay thing with the out of date SCBA tanks, like $60 plus a valve from Amazon. I've been running a pair of Yong Heng compressors for a while now and can fill the SCBA's myself, so I don't particularly care about them being out of date. At first I did, but as time has gone on, I've learned to just keep an eye on them and handle them accordingly. I use an inline regulator to fill or tether stuff that needs a lower pressure. I would imagine that the OP will arrive at this same point down the road, but in the beginning you (or at least I did) tend to go for the lower cost alternatives. Then you buy better and better stuff as you go.
Chris