Doug Fattic 

Vintage Schwinns (the ones made in Chicago) are definitely a good way to go for short trips in the city even if you don't need to use them to keep your boat from floating away. Yes they are heavy but that doesn't make them unworthy. When you pedal at a walking effort and aren't going far, they work fine. The problem (as Vintage Schwinn pointed out) is finding one in your size. They are probably in your price range. .

With your budget I also recommend (as others already have) of finding on old MTB bicycle. They have to be old enough not to have suspension forks. And probably levelish top tubes (see Bikemig's bike in post #23). Also it might be possible to find earlier models that are big. You want to find one big enough so the handlebars will be as high or higher than your seat. City biking demands that you sit more upright so you can comfortably look down the road and not worry about being aerodynamic.

Hybrids came out a bit later with skinner tires. Look for a very big one. Hybrids were not designed for serious cyclists and so won't get any respect among enthusiasts but they will do what you want. They were marketed to someone thinking they might want to get into cycling and a traditional bicycle with drop handlebars look like torture machines. They will probably work well for your purposes and be in your price range. They just won't have any coolness factor among the elites. Ignore them.