MIG is what you want, it it relatively easy to learn, and will do just about anything you need with steel. The issue with buying a welder, is you have to look at it as a long term investment. You know what you might use it for in the next year, but what about after that? Reasonable quality entry level welding set ups will set you back $400-$700. Keep in mind, you will also need small things, like a cart, a gas regulator(if not included with the welder), tank, helmet, gloves, wire, tips, and all sorts of other accessories depending on what you want to do.
Whenever this subject comes up, I almost always recommend buying something in the 120-150A range, and make sure it gas capability. You can weld with just flux wire, but it is messy, and does not like thin metals. Hobart, Lincoln, Eastwood are good brands, stay away from miller as they are top quality with a hefty price tag. I know I am going to get shot over that comment.....
Also call around your local welding supply shops and find a place that will fill your tank(s), buying the tank from them might cost a little more, but you can most likely have it swapped out on site, saving time and hassle. Airgas is decent company, thats who I use.
Here is a decent set up that I am looking at purchasing, as right now I am using a family members welder, and eventually he will want it back.
Welder with regulator
80 cubic ft argon tank-$150 initial purchase, $35 each fill
Certified auto darkening helmet-$50-75 off ebay
quality wire-$10-15 2lb spool