Well, you do have some options, but availabilty may be limited, and you just won't have as much fun but there are a few planes to look for. However, I would certainly advise spending enough to buy a full, good plane. As well as finding someone to help you learn to fly.

But, if you really can't spend more than $50 there are a few planes. I can say myself, that the FMA Direct Sksprite is a decent plane for its size. It is a very small plane with a 14'' wingspan and an odd style transmitor, but it does fly as long as there is NO wind, and it is only $35. Being an already experienced pilot, I cannot say how easy it is to learn on, but it is easy to fly, and durable, so it may be a decent choice, but keep in mind that this plane doesn't do anything spectacular, it just flies for short periods of time.

Possibly another option would a generic two engine foam planes that come with recharging stands. These are the most popular for 'sell at radioshack' type business IMO, so I wouldn't count these out, but they may turn out to be less than expected. Not sure of regional differences but these are usually in the 35-50$ range.

Remember, that these are only if you really HAVE TO only spend $50. You'll have a much better and longer lasting experience if you go with a mainstream beginning plane, and find some help to get you off the ground.