i use industrial gasses.
£60 at year for the bottel + £27.50 for refills
when you conider those littel bottels only hold 60 ltrs of gas. your going to be useing 6-10 ltrs minute there only goood for 6-10 minutes welding and they weep like hell anyway.
big bottels are much cheeper and your not worried about runnign out of gas so you don't get sh!t welds from skimping on gas.
i think CO2 has it's place but it will splatter like hell but it's incredibly cheep, it's good for filling chassi rails ect to prevent fire's but as a primary sheild it's not very good for small welders, beig welder cope with it much better but welds arn't as nice as with argon