There are things to be considered when buying a TIG machine. If you want to produce quality welds but want to get a machine for 400 bucks, forget it. Buy a dedicated tig machine WITH the foot amperage control. Some of the cheaper priced machines do not have this option. You set the amperage and the tungsten is immediately hot. 
  With the foot control, power is availible as you depress the pedal. This prevents flash from a 135 amp setting when the electrode approaches the workpiece.  Also, what makes a good machine is not how high it goes but it's performance on the low settings, especially in AC/High frequency.  Most reputable dealers with showrooms have demonstrators for a guy to see and try out. Even if you do not buy from that dealer, you still know what you are buying. Better quality machines have post flow adjustments for the gas too. Some machines have this fixed and as high as 25 seconds too. This becomes wasteful with this rate of consumption of gas.

 Remember, buy what you need, not what you want. Don't settle for what you don't want. Save your bucks and get the good one to begin with.

 Hope this helps!

Mike

p.s. feel free to drop me a line with any questions.