If you want to weld alloy you need AC tig capability - all of those inverters look to be DC only.
I'd strongly recommend not buying a new chinese machine from Trademe, unless the seller can supply parts and warranty. You might end up spending on a tig only for a circuit board to blow in 6 months, leaving you up shit creek.
Most AC/DC tig units start around the $2g mark for a decent one. That gets you everything you need to get started apart from Argon - they normally come with an arc handpiece as well. Also for Aluminium you'll want around 200A IMO, so that you can do thicker stuff like pleniums and big alloy brackets.