try a couple of NRF2401 breakout boards with preamps, LNA's, and external antennae. There's a guy on this forum who sells good ones. Then go to GearBest or BangGood and get a 2W 2GHz linear amp for the xmit side. look up some good antennae. That's the EASY part.
After that, and you have wasted a bunch of time and effort (but maybe learned some things), study up on open source flight controllers.