I want a cheap bicycle to get around Buenos Aires. About how much could I expect to pay?

I'll be living somewhere in the Belgrano/Palermo area. First of all, actually, if I were to get a bicycle, would that be a safe option for getting around or is street traffic too dangerous for cyclists? And second, how much would it cost to buy a cheap bike, not necessarily brand new. Would it be possible to get one for under $50 USD?