+1 on the Earthquake for value. That's what this thread is all about - the best for under $100. Is the Earthquake gun the best, probably not, but it's great for the money.
My earthquake gun set on 4 (out of 6 settings) when tightening down and just stops moving puts lug nuts on my Chevy truck JUST shy of 110 ft. lbs, and then I torque them with a torque wrench. Doing the same thing with it set to 6 is WAY more than 120 ft. lbs. It doesn't even work taking lug nuts off of anything I've tried it on. My uncle has a few of the Earthquake guns in his Agriculture equipment shop, and those guys love them. The only downside is weight - they're hefty. But I don't consider that a weakness - it ain't gonna break if/when you drop it either.
My compressor is a 2HP peak (probably 1hp actual) 21 gallon oil-filled 125psi max unit rated at 4cfm at 90psi. It runs it fine on 50 ft of 3/8" hose. FORGET about the coily-hoses (as mentioned earlier), they're usually only 1/4" and won't come close to running ANY impact. If you have trouble, question the flow of your regulator if you have one installed (and especially if it came on the compressor). The one that came on mine could be set to 90psi, but when flowing, pressure would drop to 40psi, and I had no power. I took it out of line, and run tank pressure at about 120, which is 85-90 psi when flowing on the end of the 50ft 3/8" hose...perfect!