absolutely everything, there's some common ground station stuff (your handheld transmitter, and goggles or 7" LCD monitor + video receiver), that's an unavoidable upfront cost separate from the aircraft itself. Figure at minimum $300 to $400 for that.

For a small quadcopter, $400-500 total parts cost, anything below that will involve a lot of quality compromises.

Take a look at some of the RTF / ready to fly specifications sold by getfpv.com or helipal.com for examples.