Google online about bike sizes and figure out what size frame you need. That will help greatly to narrow the choices of craigslist. Otherwise for $200 you are going to end up with a bike from Walmart or target, which will be very poor quality. Better to take sometime to educate yourself about what would be a good choice and find something on Craigslist.
When searching Craigslist, in the bike section, enter your frame size - that will bring up a list of appropriately sized bikes. For instance, I need a 54cm bike so I put "54" into the search box. If you are 5'4" you probably need a 52cm bike frame. Look over the bikes carefully, do a test ride. Don't buy a rusty bike.
There is a blue book for used bike values (google) that can be helpful too.