The more user friendly you go, the more expensive the solution is. For $3,000 US you can buy an Event 38 E384 fixed wing that can do optical and NDVI imagery. You currently need to be somewhat technically proficient to use it.
For, I think, $16,000 US you can buy an AgEagle or SenseFly eBee. These are much easier to fly and collect very similar imagery.
If you want to fly a wider variety of sensors, check out PrecisionHawk. The airframe is about $16,000 and sensors range from $1,000 to $10,000 depending on what you want to do.
My favorite Quadcopter for overall outside use is 3D Robotics SOLO The Smart Drone is the first Drone made for your GoPro and you can get it at Best Buy.