I want to buy a bike so I can go casually riding with my girlfriend, but I'm looking at a budget of around $150. I really don't want to spend too much on it if I don't have to, because I'm a student and money is tight, so is there anything around that price range that doesn't totally suck? If absolutely necessary I suppose I would be willing to go to $200, but I would probably rather go with a used bike instead to lower the price. Any ideas, brands, models, or general advice? I know nothing about bikes, so any advice is appreciated!