I bought a air rifle SCBA tank and I can get 10,000 shots with a match rifle per fill up. I also lucked into a high pressure gasoline SCBA compressor so I am set. But really you only need a 4500psi/300BAR scba tank, and most fire departments will fill you up for a small donation. Even a SCBA tank is a ton cheaper than 22s.
Another option is a 3300 psi scuba tank, they are cheap. Use that tank, and top off with a hand pump. Hand pump necessarily have a lot more moisture than a compressed tank. Some airgun manufactures prohibit hand pumps and using one will void warranty.