$100-$200 may not net much in the SF Bay area, I dunno, we've some regular posters from there; it seems like the prices are generally higher fof decent stuff.

I'd avoid the electro-forged Schwinns (Varsitys, in particular) because they weigh a ton. You'll notice it if you have hills on your commute. Plus, see (1) below.

Aside from the sizing info, here's some tips:

1) Avoid steel rims. Although they can be upgraded, they're heavy, and the upgrade may cost more than the bike. Weight on the edge of the wheel has a disproportiate affect on a bike. In addition, steel rims result in poor braking, except in wet weather, when they result in no braking. If in doubt, use a magnet.

2) Most bikes in your range are gonna be steel framed anyhoo. Look for tubing stickers, generally anything double butted isn't a bad sign.

3) In my expereince, LBSs vary wildly in response to older bikes. Some will just try to sell you a new bike, as you used one is woefully inadequate (it's not). Some will be clueless about various repair issues, because they never see cotter pins or French threadings or old Raleighs or Three speed hubs or whatever. Ask around locally, some commuters and riders can prolly make decent recomendations.

4) Try to get a bike with cotterless three piece cranks. Easier to overhaul for most shops and for newbies, assuming you'd like to work on it yourself.

5) If it's on CL and they don't let you ride it first, don't buy it.

6) Buy a good repair manual. Zinn and the art of Road Bike Maintenance is fine. However, old editions of Richard's Bicycle Book (Ballantine books) have an excellent basic repair section, showing how to handle most jobs with basic tools. I also liked Bill Walton's Complete book of Bicycling (yes, that Bill Walton) but it's not as easy to find.