Don't buy a Harbor Freight!!

I bought a Lincoln SP135 and really like it and it will do anything you need to weld on your project. You will want to use a 75/25 mix of argon and CO2. Straight CO2 is cheaper but produces a lot more splatter and equates to more cleanup.

Don't use self shielding wire, too messy of welds and makes welding thin panels somewhat difficult.

Below is a link for one from Eastwood that is worth checking into. The price is very reasonable for a mig welder for what you are describing.

http://www.eastwood.com/mig-welder-110vac-135a-output.html