shame i didn't see this earlier- i had an arc welder i took to the tip, paid £40 for it years ago, just didn't use it anymore… arc is good for anything over 3mm really… i bought a 2nd hand mig for £100 and it works pretty well on stuff over 2.5mm up to 4mm and is much easier to learn than arc.

If you do go for mig dont bother with the gasless systems, their pretty rubbish.

As Gary pretty much said though a TIG is one of the best workshop investments you can make.