I think for $100 you stole it! Most likely, you will just need to adjust the shifter cable to fix your shift issues. Sheldon will tell you how:
http://sheldonbrown.com/sturmey-archer/adj.html
That's a great bike, enjoy it!
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1964 JRJ (Bob Jackson), 1973 Wes Mason, 1974 Raleigh Gran Sport, 1986 Schwinn High Sierra, 2000ish Colian (Colin Laing), 2011 Dick Chafe, 2013 Velo Orange Pass Hunter