will you be taking the BART? will you be into cycling outside of work commutes? etc etc various factors 150 - 200 isn't very realistic maybe if you buy second hand but even then... if you're starved for space a folder would be a good idea, mountain bikes are very comfortable and easy to ride, single speeds are fun and road bikes are quick and nimble, depending on your budget giant, trek, gary fisher, cannondale make excellent commuter bikes, if you're looking for folders to carry on the BART dahon and swift make some highly acclaimed models, what i recommend is go a little over your budget and get something good, don't do what i did and try to pinch pennies, get addicted to cycling then waste a whole bunch of money in the end selling and upgrading
just my 2 cents
I'm not sure if I'll be using the bike outside of work commutes. I imagine I'd prefer biking on roads as opposed to dirt paths, but I really can't say for sure. I don't need a folder. I think there are plenty of safe places to put the bike in my apartment building/at work.
What price gets me something good? Would $300 get me something worth keeping?