You'd be ok with a cheap anything as long as you are smart about how you ride.

My 45 year old stepmom started out on a HD Heritage Softail, which is a 1450 (or something crazy like that) and it weighs around 800 lbs. She has done very well just because she's careful.

The bike you get depends on you and your tastes and what you want from a bike. A 500 cc bike will most likely be too slow for most people.