You could have a lot of fun in that area with a cheap, toy-grade quad. Once you get past the hover, go out, come back, left and right stage and decide you want to fly it around like a plane, you'll have a better understanding of the available airspace and potential hazards.
You could be fairly confident that if the area is too small to comfortably fly a little quad around in, it is way to small for most RC planes. If you're cruising around with no problem, then you could look into ramping it up with a Mighty Mini. I haven't the skill to do it yet, but many of them are fully capable of slow, low and close.