Mark I would stay away from SIP mig welders, i've read far too many posts of people having bad experiences with them, they are no longer built like they used to be.
People recommend Clarke mig welders to start with as they are cheap and are good quality for a budget hobby welder. I personally have a Clarke 150EN, which I managed to pick up for £85, it just needed a few new bits for it (a new gas valve and swan neck), gas regulator and then the consumables on top of that.
If you pop over to the mig welding forum (
Link).