MIG will only give a good weld if you are a good welder.

Get a cheap arc welder. I bought a dirt cheap one from macro for around £30. Did me well for a good few years then it went on to Jamie. Arc will do hardox fine.

Don't bother with MIG or TIG unless you go for a gas setup as the gasless stuff is crap. If you can get a decent weld with a cheap arc welder then it will set you up well to spend a bit more on a decent setup down the line.

Your other option is to look on gumtree for a cheap second hand one.