Perhaps give away a drone to a second and third place winner as well. Drones for them could be the DJI Phantom 3 4K which can be hard for $600 while the first place winner get a more expensive drone. Obviously easier said then done since it'll be a bit expensive to give away 3 drones. Still, if the budget was say $3,400 for a single drone (Which can get you an Inspire 1 Pro with the standard X5 camera), decrease it to around $1,149 to $1,600 (Which can get you either a Phantom 4, Typhoon H or Typhoon H Pro) and you'll be able to offer 2 other drones.