not too much really. power. 200A gets you pretty far, but 100 isn't enough for some things. if you don't get AC you can't weld aluminum. without a water cooler

not too much really. power. 200A gets you pretty far, but 100 isn't enough for some things. if you don't get AC you can't weld aluminum. without a water cooler you have to make sure not to run the head too long without a break, but for personal use its not too bad. if you get one without the argon valve and control its a pain, but its usable (you have to stopcock open the argon before use and turn it off, so you go through more gas). cheaper ones might not have the HF start so you need to scratch start, which is a pain, but livable. the only thing to really be wary about with the cheaper deals is that they often don't include the head, sleeve, controls, ground clamp, argon fittings and regulator. so those might add some hidden cost. regardless you need to budget another ~$300 for a tank and gas. but the difference between low end and low end professional is alot of money, so I would definitely recommend skimping a little. since the tips are consumed there isn't much of a wear issue really. a super cheap option is a used stick machine with a tig head if you can live with all of the above limitations. if you upgrade you can carry forward the tank, regulator and head.