You're barking up the wrong tree looking at small MIGs like that if you want to be welding 6mm. If it's mainly thicker type material, angle iron etc, and you don't need to be welding any very thin sheet, go for an Arc Welder. Not as easy to learn, but less to run (no gas involved), more versatile on thicker materials, and you will get a set within budget that could weld well over 6mm.