At your height I wouldn't go smaller then 650 and would suggest a 750. Now with that in mind, not be familiar with these bikes and what to look for you may get hosed the first time you buy one. Don't let it discourage you though it has happenned to, if not all, than most of us. If I were in your shoes I would buy one in the 800 - 1500 range. Here you should be able to have a ridable CB, even if you have to do some tweeking. You will want to check the compression, timing, and you will most likely have to rebuild the carbs and adjust your valves. While this may sound like quite a bit, it is pretty easy to do, and if you run into any problems you will find plenty of help here.
My main suggestion would be take your time and shop around. We have all gone to look at a bike, started drooling and bought it, only to find later we had made a mistake.
Hey you never know, you can really score as well, I bought my 73 CB500 for 400 dollars, the PO thought it was toast.
It cost me 150 dollars in parts and I have one of the best running bikes I've ever owned.
Lastly feel free to bounce ideas off of us, find a bike and give us the run down, I'm sure someone will give you their 2 cents and maybe be able to give you an idea of what a bike may be worth(include pics, makes it easier).
Happy hunting.