Not sure over what timespan you've done those 10hours of welding?
you're usage is most likely far higher than most hobbyists and you'll almost definately save money on your argon costs by going over to a full size boc W cylinder or similar from air products etc.
We have just this week got these new regs and worked out you get roughly a 40% gas saving (worked out on a MIG set up). We had a deal on them from our welding supplier as bought a plasma cutter at the same time and they were under £100, but I think they can be bought individually for about £150, but the saving on gas pays for them in no time!