Welding takes a lot of practice to get good at, especially if you don't have anyone to teach you. If you can get a class at a local junior college, it would probably save you a lot of pain and agony of trail and error. However, it's totally doable on your own if you are handy. I would check out some of the resources from welding giants like Miller or Lincoln, they have instructionals on what makes a good bead, and a lot of welding forums also have lots of tips.
Since you want to weld material under 1/4" thick, your best bet for the money is going to be a MIG welder WITH a 75/25 Argon/CO2 mix. Welding with a flux core setup, while cheaper, gives you a hell of a mess, and it's hard to weld thin material (you will blast right through too easily). I recently bought a Hobart 120v MIG welder, and I couldn't be happier for my application. It does anything up to 1/4" with enough adjustments for what I need. I welded my 3-tier tower with it using 16ga box tubing.
It's going to be hard to put together a set of gear for less than $1000. A decent welder will cost at least $500, factor in a welding mask, solid wire (usually .030), welding tips (a new welder usually comes with a few), welding gloves, welding tank, regulator and hose, and welding clamps/magnets, you are looking at a pretty penny, unless you can find someone to get it all from second hand.
Here's a link to the welder I have, for the money it's a great buy.
http://www.tractorsupply.com/hobart-handler-reg-140-mig-welder-3812040
You don't need anything bigger than that.
