I've just bought a disposable bottle and it has 60 cubic litres of gas. And i turned my gas flow metre down to 1 to 2 litres a minute and it welded fine. So it should last at least 30 minutes.
I bought my welder from Tokentools. fully adjustable, pulse, power slopes, etc. great welder for only $600 including flow meter and freight.
WWW.tokentools.com.au.
160 amps model TT tig160P.
JD