I'm shocked that nobody said "buy an old honda".
You can't go wrong. It will be cheap, and you will lay it down (or a buddy will). The old inline 4's are no joke. A 650 or 750 nighthawk would be a great choice. Most are shaft drive six speeds that run forever or just need new carbs, It's an upright bike that handles like a sportbike. Pre-1990 will be less than a grand and you won't feel bad leaving it in the rain. When you've gotten it figured out go buy a decent bike and keep the cheap one for friends or springtime riding. If you want sprt go nighthawk or v45 sabre.
I bought a v45 magna (83 I think) for $600 bucks last summer (came with suit, helmet, and leather jacket). Liquid cooled, shaft drive, six speed. It does 80 in third gear. It's light enough that I can toss it around on corners and a blast to ride. At 700 or 750cc I can't think of a better starter bike (cruiser style-low center of gravity). They run about 80-90 horse if I recall; respectable. It'll do 120 if you want but I've never needed to.
The other v-4's (vfr1000 or v65 magnas or sabres) can be had for $1,500 or less and will napalm anything but a litre bike (or an old v-max; that'll come down to the rider). I've had my v65 just shy of 140 and it still had throttle left.
Get a cheap fun starter. You'll be glad you did.
my .02- Josh