* A work of art that's appraised at $10,000, for example, but that's priced for sale at $5000, is not necessarily a bargain. As stated above, a retail or insurance appraisal can be many times the fair market value of a work of art. Always determine fair market value first, no matter how big a bargain the seller makes you think you're getting.
In general the aircraft must be at least 500 feet away from any person, vessel, vehicle, or structure. In congested areas the aircraft must stay 1000 feet above the highest obstacle within a 2000 foot radius of the aircraft. There are special rules for helicopters that allow them to fly closer than these general limits.
The first and most obvious limit to how low airplanes can fly is the ground. In aviation, there are two standards for measuring altitude: height above sea level and height above the ground. Height above sea level establishes an unchanging standard, which simplifies communications between pilots and controllers, as well as pilots and other pilots.