I'd have to say your best option would be the Parrot AR Drone. It's probably will be higher than your price range but it's definitely worth it. I personally have one and have even programmed it to dance to music. It's extremely easy to work with and there are numerous libraries out there for most languages. I highly recommended it, you don't even need to modify the drone to start developing for it. I've built my own quadcopter and would have to say I still prefer the AR Drone when it comes to development.