This is hypocritical, but I find four wheelers to be dangerous, at least in comparison. They're good tools, but I don't like getting crazy on them. Working the bars will beef up your upper body quick as well.
For $1500, I'd find an old UJM and do a light restoration on it, or make it a scrambler or something.
For that kind of money if you want a bike that's ready to go, get an old XL or some other dual sport though.