It is possible to get a 300 bar compressor that plugs into the mains for around £1300 new, only £650 if you use 232 bar.
But the best way is a dive bottle, filled from a scuba centre, and the bottles skeetmaster is offering are good value. You will still need a fill rig, to transfer the air to the guns bottle.
A lot depends on your needs when you play, front player, back player, rec-ball, and what is available regarding air at the site you play.
If you decide to get a compresser, check your insurance covers the use of such an item, because 300 bar is an exremely high pressure, and can be very dangerous.